cbfs: more accurate size check for simple buffer mapping

cbfs: more accurate size check for simple buffer mapping

currently, if the cache size is, for example, 4096 byte, mapping 4096 byte data
fails due to the overly strict check. this change allows cbfs_simple_buffer_map
to use all the cache space to the last byte.

BUG=None
TEST=Booted Nyan Blaze.
BRANCH=None
Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Original-Change-Id: I0797b5010afd7316fdec605784e8f48e2d62c37f
Original-Reviewed-on: https://chromium-review.googlesource.com/218883
Original-Commit-Queue: Daisuke Nojiri <dnojiri@chromium.org>
Original-Tested-by: Daisuke Nojiri <dnojiri@chromium.org>
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
(cherry picked from commit b0b31da336fa2f87fe73f063782d6243f8262d10)
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Change-Id: I15e11e574cd14484fe83c9c3674bb5c2d14422f6
Reviewed-on: http://review.coreboot.org/9178
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>