[XFS] Kill direct access to ->count in valusema(); all we ever use it for

is check if semaphore is actually locked, which can be trivially done in
portable way. Code gets more reabable, while we are at it... 

SGI-PV: 953915
SGI-Modid: xfs-linux-melb:xfs-kern:26274a

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Nathan Scott <nathans@sgi.com>