x86: rename after_init_bootmem to after_bootmem in mm/init_32.c

Impact: cleanup

This patch renames after_init_bootmem to after_bootmem in
mm/init_32.c to reduce the diff to the 64-bit version of of
init_memory_mapping().

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1236257708-27269-7-git-send-email-penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>