tpm2: refactor tpm2 return value processing
tpm2: refactor tpm2 return value processing

There is no point in checking and reporting error code in each
function calling tpm_process_command(), let's do it in one place for
all commands.

BRANCH=none
BUG=chrome-os-partner:50645
TEST=Kevin still boots to chrome os

Change-Id: I10f45bd15df293f63401c295c5dce833543c50da
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/358174
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>
Reviewed-by: Darren Krahn <0c011cef6b0a329cf1a859e1450ec8a1be7f57d9@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot