[CIFS] Change semaphore to mutex for cifs lock_sem

Originally at http://lkml.org/lkml/2006/9/2/86



The recent change to "allow Windows blocking locks to be cancelled via a
CANCEL_LOCK call" introduced a new semaphore in struct cifsFileInfo,
lock_sem.  However, semaphores used as mutexes are deprecated these days,
and there's no reason to add a new one to the kernel.  Therefore, convert
lock_sem to a struct mutex (and also fix one indentation glitch on one of
the lines changed anyway).

Signed-off-by: Roland Dreier <roland@digitalvampire.org>
Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>