gsctool: Add error code description if authcode fails.
gsctool: Add error code description if authcode fails.

When doing RMA reset and the auth code is rejected, gsctool only reports
the error code, which is not clear for the user. This CL adds the
failure reason to make the message clearer.

BUG=b:128801501
TEST=make gsctool; manually test on DUT
BRANCH=none

[Before fix]
localhost $ gsctool -a -r "A"

rma unlock failed, code 1
Processing response...

localhost $ gsctool -a -r "ABCDEFGH"

rma unlock failed, code 6
Processing response...

[After fix]
localhost $ gsctool -a -r "A"
Processing response...

rma unlock failed, code 1 (wrong authcode size)

localhost $ gsctool -a -r "ABCDEFGH"
Processing response...

rma unlock failed, code 6 (authcode mismatch)

Change-Id: I5db4d8f7cffe5b582f48fdc3b7fb27493b3715ff
Signed-off-by: Cheng-Han Yang <aa3f9ca10b2feb66c71f30ed833925f3c565934a@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1527905
Commit-Ready: Cheng-Han Yang <aa3f9ca10b2feb66c71f30ed833925f3c565934a@chromium.org>
Tested-by: Cheng-Han Yang <aa3f9ca10b2feb66c71f30ed833925f3c565934a@chromium.org>
Reviewed-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>

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