uartupdatetool: retry opr_check_sync() if the first attept fails
uartupdatetool: retry opr_check_sync() if the first attept fails

This is a workaround fix for grunt, where the first command after EC
reset gets zero bytes as response.

BUG=b:126795953
BRANCH=none
TEST=manually ran flash_ec on grunt/careena, grunt/liara and
octopus/fleex through servo_v4_with_ccd_cr50 or suzy-Qable.

Change-Id: I5da3bd7889d9e4059a8f523352db4f3e5a7ce841
Signed-off-by: Namyoon Woo <e8732cefb861f07768f47df788a8e8eb75efc09a@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1583128
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Reviewed-by: Raul E Rangel <9a9c998e11a2655b1de9a05eeeef5f710c0dc7ed@chromium.org>

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