NAND: fix some strict-aliasing compiler warnings

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/common/env_nand.c b/common/env_nand.c
index ce0a251..b6a5b4a 100644
--- a/common/env_nand.c
+++ b/common/env_nand.c
@@ -154,7 +154,7 @@
 #ifdef CFG_ENV_OFFSET_REDUND
 int saveenv(void)
 {
-	ulong total;
+	size_t total;
 	int ret = 0;
 
 	env_ptr->flags++;