alpha: fix bitops

Documentation/atomic_ops.txt defines these primitives must contain a memory
barrier both before and after their memory operation.  This is consistent with
the atomic ops implementation on alpha.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>