fpga: Avoid ignored-qualifiers warning

Fixes annoying warnings of the following type when built with W=1 (for
each file including fpga.h):

      CC      drivers/fpga/fpga.o
    In file included from /mnt/data/adahl/src/u-boot/include/xilinx.h:7,
                     from /mnt/data/adahl/src/u-boot/drivers/fpga/fpga.c:10:
    /mnt/data/adahl/src/u-boot/include/fpga.h:61:1: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
       61 | const fpga_desc *const fpga_get_desc(int devnum);
          | ^~~~~
    /mnt/data/adahl/src/u-boot/include/fpga.h:81:1: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
       81 | const fpga_desc *const fpga_validate(int devnum, const void *buf,
          | ^~~~~
    /mnt/data/adahl/src/u-boot/drivers/fpga/fpga.c:36:1: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
       36 | const fpga_desc *const fpga_get_desc(int devnum)
          | ^~~~~
    /mnt/data/adahl/src/u-boot/drivers/fpga/fpga.c:53:1: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
       53 | const fpga_desc *const fpga_validate(int devnum, const void *buf,
          | ^~~~~

Do some type and cast cleanup on that fpga_desc type while at it.

Link: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wignored-qualifiers
Signed-off-by: Alexander Dahl <ada@thorsis.com>
Link: https://lore.kernel.org/r/20250121162213.1477506-1-ada@thorsis.com
Signed-off-by: Michal Simek <michal.simek@amd.com>
diff --git a/drivers/fpga/fpga.c b/drivers/fpga/fpga.c
index 1f67825..f88267e 100644
--- a/drivers/fpga/fpga.c
+++ b/drivers/fpga/fpga.c
@@ -33,9 +33,9 @@
 /* fpga_get_desc
  *	map a device number to a descriptor
  */
-const fpga_desc *const fpga_get_desc(int devnum)
+const fpga_desc *fpga_get_desc(int devnum)
 {
-	fpga_desc *desc = (fpga_desc *)NULL;
+	const fpga_desc *desc = NULL;
 
 	if ((devnum >= 0) && (devnum < next_desc)) {
 		desc = &desc_table[devnum];
@@ -50,8 +50,8 @@
  * fpga_validate
  *	generic parameter checking code
  */
-const fpga_desc *const fpga_validate(int devnum, const void *buf,
-				     size_t bsize, char *fn)
+const fpga_desc *fpga_validate(int devnum, const void *buf,
+			       size_t bsize, char *fn)
 {
 	const fpga_desc *desc = fpga_get_desc(devnum);
 
@@ -60,7 +60,7 @@
 
 	if (!buf) {
 		printf("%s: Null buffer.\n", fn);
-		return (fpga_desc * const)NULL;
+		return NULL;
 	}
 	return desc;
 }
@@ -72,7 +72,7 @@
 static int fpga_dev_info(int devnum)
 {
 	int ret_val = FPGA_FAIL; /* assume failure */
-	const fpga_desc * const desc = fpga_get_desc(devnum);
+	const fpga_desc *desc = fpga_get_desc(devnum);
 
 	if (desc) {
 		debug("%s: Device Descriptor @ 0x%p\n",
@@ -374,7 +374,7 @@
 #if CONFIG_IS_ENABLED(FPGA_LOAD_SECURE)
 int fpga_compatible2flag(int devnum, const char *compatible)
 {
-	const fpga_desc * const desc = fpga_get_desc(devnum);
+	const fpga_desc *desc = fpga_get_desc(devnum);
 
 	if (!desc)
 		return 0;