pe_vdm_request_run: Refactor NAK/BUSY handling
pe_vdm_request_run: Refactor NAK/BUSY handling

Eliminate a redundant layer of checks.

BUG=none
TEST=make buildall
BRANCH=none

Signed-off-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>
Change-Id: Iae5da3a6bb5efddafab03d752e7079a67543cf46
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2234803
Reviewed-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>

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