env_nand: zero-initialize variable nand_erase_options

Commit 30486322 (nand erase: .spread, .part, .chip subcommands)
added a new field to struct nand_erase_options, but forgot to
update common/env_nand.c.

Depending on the stack state and bad block distribution, saveenv()
can thus erase more than CONFIG_ENV_RANGE bytes which may corrupt
the following NAND sectors/partitions.

Signed-off-by: Daniel Hobi <daniel.hobi@schmid-telecom.ch>
Signed-off-by: Scott Wood <scottwood@freescale.com>

common/env_nand.c

@@ -193,10 +193,8 @@ int saveenv(void)
 	int	ret = 0;
 	nand_erase_options_t nand_erase_options;
 
+	memset(&nand_erase_options, 0, sizeof(nand_erase_options));
 	nand_erase_options.length = CONFIG_ENV_RANGE;
-	nand_erase_options.quiet = 0;
-	nand_erase_options.jffs2 = 0;
-	nand_erase_options.scrub = 0;
 
 	if (CONFIG_ENV_RANGE < CONFIG_ENV_SIZE)
 		return 1;
@@ -249,10 +247,8 @@ int saveenv(void)
 	char	*res;
 	nand_erase_options_t nand_erase_options;
 
+	memset(&nand_erase_options, 0, sizeof(nand_erase_options));
 	nand_erase_options.length = CONFIG_ENV_RANGE;
-	nand_erase_options.quiet = 0;
-	nand_erase_options.jffs2 = 0;
-	nand_erase_options.scrub = 0;
 	nand_erase_options.offset = CONFIG_ENV_OFFSET;
 
 	if (CONFIG_ENV_RANGE < CONFIG_ENV_SIZE)