[PATCH] coredump_wait() cleanup

This patch deletes pointless code from coredump_wait().

1. It does useless mm->core_waiters inc/dec under mm->mmap_sem,
   but any changes to ->core_waiters have no effect until we drop
   ->mmap_sem.

2. It calls yield() for absolutely unknown reason.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>