[XFS] lock validator: lockdep: small xfs init_rwsem() cleanup

init_rwsem() has no return value.  This is not a problem if init_rwsem()
is a function, but it's a problem if it's a do { ...  } while (0) macro. 
(which lockdep introduces) 

SGI-PV: 904196
SGI-Modid: xfs-linux-melb:xfs-kern:26082a

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Nathan Scott <nathans@sgi.com>