cgpt_wrapper: Fix non-zero return code when okay
cgpt_wrapper: Fix non-zero return code when okay

I forgot to reset "ret" to zero in the case the two hashes come out the
same. This CL fixes that silly logic bug.

BUG=None
BRANCH=None
TEST=`cgpt show /dev/mtd0` should exit with status 0

Change-Id: I1c64ea215c861c8afb44e235d090c72a5d006d55
Reviewed-on: https://chromium-review.googlesource.com/243325
Reviewed-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Commit-Queue: Nam Nguyen <c26e2a6964d90b41b9eabeee8eb089881ad2e039@chromium.org>
Trybot-Ready: Nam Nguyen <c26e2a6964d90b41b9eabeee8eb089881ad2e039@chromium.org>
Tested-by: Nam Nguyen <c26e2a6964d90b41b9eabeee8eb089881ad2e039@chromium.org>

geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,acorn-marvell/vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,coreboot/vboot,acorn-marvell/vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference