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/arch/arm/cpu/arm926ejs/mxs/mxs.c b/arch/arm/cpu/arm926ejs/mxs/mxs.c
index 365542f..ef130ae 100644
--- a/arch/arm/cpu/arm926ejs/mxs/mxs.c
+++ b/arch/arm/cpu/arm926ejs/mxs/mxs.c
@@ -83,7 +83,9 @@
 	int i;
 
 	for (i = 0; i < 8; i++) {
+		/* cppcheck-suppress nullPointer */
 		vt[i] = ldr_pc;
+		/* cppcheck-suppress nullPointer */
 		vt[i + 8] = start_addr + (4 * i);
 	}
 }