Fix update out-of-bounds check for partition boundary.

This is an off-by-one error caught during the implementation of unit
tests.

BUG=None
TEST=Unit tests (upcoming) pass as expected.

Change-Id: I9a5da10588f0ac4314e9a35280ff1f38c34c88ac
Reviewed-on: https://gerrit.chromium.org/gerrit/44953
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
1 file changed