fs/partitions/check.c: make local symbols static

The symbols part_ro_show, part_alignment_offset_show, and
part_discard_alignment_show are not used outside this file and
should be marked static.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>