x86, mpparse: Put check_slot() into .init section

check_slot() is only called from replace_intsrc_all() - which is
in the .init section.

So, put check_slot into the .init section as well, so it can be freed
after system boot.

Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
LKML-Reference: <AANLkTing52ntzRcHkODCWDKOfRF=0uhXw5-cCUhx6M54@mail.gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>