uboot-imx

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>