fdt: Swap the signature for board_fdt_blob_setup()

This returns a devicetree and updates a parameter with an error code.
Swap it, since this fits better with the way U-Boot normally works. It
also (more easily) allows leaving the existing pointer unchanged.

No yaks were harmed in this change, but there is a very small code-size
reduction.

For sifive, the OF_BOARD option must be set for the function to be
called, so there is no point in checking it again. Also OF_SEPARATE is
defined always.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Matthias Brugger <mbrugger@suse.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
[trini: Update total_compute]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
index 9122f33..c46fe4b 100644
--- a/board/raspberrypi/rpi/rpi.c
+++ b/board/raspberrypi/rpi/rpi.c
@@ -508,15 +508,14 @@
 /*
  * If the firmware passed a device tree use it for U-Boot.
  */
-void *board_fdt_blob_setup(int *err)
+int board_fdt_blob_setup(void **fdtp)
 {
-	*err = 0;
-	if (fdt_magic(fw_dtb_pointer) != FDT_MAGIC) {
-		*err = -ENXIO;
-		return NULL;
-	}
+	if (fdt_magic(fw_dtb_pointer) != FDT_MAGIC)
+		return -ENXIO;
+
+	*fdtp = (void *)fw_dtb_pointer;
 
-	return (void *)fw_dtb_pointer;
+	return 0;
 }
 
 int copy_property(void *dst, void *src, char *path, char *property)