cppcheck cleanup: fix nullPointer errors

There are a number of places where U-Boot intentionally and legally
accesses physical address 0x0000, for example when installing
exception vectors on systems where these are located in low memory.

Add "cppcheck-suppress nullPointer" comments to silence cppcheck
where this is intentional and legal.

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/board/esd/pci405/cmd_pci405.c b/board/esd/pci405/cmd_pci405.c
index 55c20d0..29c688a 100644
--- a/board/esd/pci405/cmd_pci405.c
+++ b/board/esd/pci405/cmd_pci405.c
@@ -23,7 +23,7 @@
  */
 int do_loadpci(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
-	unsigned int *ptr = 0;
+	unsigned int *ptr;
 	int count = 0;
 	int count2 = 0;
 	int i;
@@ -35,12 +35,14 @@
 	 * Mark sync address
 	 */
 	ptr = 0;
+	/* cppcheck-suppress nullPointer */
 	*ptr = 0xffffffff;
 	puts("\nWaiting for image from pci host -");
 
 	/*
 	 * Wait for host to write the start address
 	 */
+	/* cppcheck-suppress nullPointer */
 	while (*ptr == 0xffffffff) {
 		count++;
 		if (!(count % 100)) {