semaphore: __down_common: use signal_pending_state()

Change __down_common() to use signal_pending_state() instead of open
coding.

The changes in kernel/semaphore.o are just artifacts, the state checks are
optimized away.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>