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/scb9328/flash.c b/board/scb9328/flash.c
index e3a582f..73bfa00 100644
--- a/board/scb9328/flash.c
+++ b/board/scb9328/flash.c
@@ -72,8 +72,10 @@
 
 	FLASH_BUS *addr = (FLASH_BUS *) 0;
 
+	/* cppcheck-suppress nullPointer */
 	*addr = FLASH_CMD (CFI_INTEL_CMD_READ_STATUS_REGISTER);
 
+	/* cppcheck-suppress nullPointer */
 	return *addr;
 }