__clear_bit_unlock does not need to perform atomic operations on the
variable.  Avoid a cmpxchg and simply do a store with release semantics.
Add a barrier to be safe that the compiler does not do funky things.

Tony: Use intrinsic rather than inline assembler
Signed-off-by: NChristoph Lameter <clameter@sgi.com>
Acked-by: NNick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NTony Luck <tony.luck@intel.com>