rma_reset: fix board ID ordering and add the missing break
rma_reset: fix board ID ordering and add the missing break

The Board ID is stored in Cr50 in reversed byte order, make sure it is
used in the challenge calculation in the same form.

BRANCH=none
BUG=b:37952913
TEST=verified that the proper byte order is used when challenge source
     is created.

Change-Id: I6c6b46431005ce9438a4be9aa43aafed30a645aa
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/693615
Reviewed-by: Michael Tang <58a16ebeee4f98a93729a0a09644ee723b9624f1@chromium.org>

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