modpost: Make section mismatches an error

If any section mismatches are detected the compilation will fail.
Section mismatches can go back to being warnings with
CONFIG_NO_ERROR_ON_MISMATCH=y.

Change-Id: I44f01f348703d2fdda77f2930bc290f6867b5b08
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
(cherry picked from commit d34cd35c3aacb219de789a61a140e7f095794a3f)
[stepanm@codeaurora.org: resolve minor conflict]
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>