iteflash: tweak verify_flash()
iteflash: tweak verify_flash()

There is no point in comparing read buffer with the file contents in
case flash contents read back failed.

BRANCH=none
BUG=none
TEST=verified that running

   $ make BOARD=dragonegg -j
   $ ./util/flash_ec --board=dragonegg

   still succeeds when servod is running and the DUT is connected
   through the servo-v2 board.

Change-Id: I8cd33140be4e834490b368df58aa2fd4546fe280
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1266676
Reviewed-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec