dlm: fix plock dev_write return value

The return value on writes to the plock device should be
the number of bytes written.  It was returning 0 instead
when an nfs lock callback was involved.
Reported-by: Nathan Straz <nstraz@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/plock.c

@@ -379,7 +379,7 @@ static ssize_t dev_write(struct file *file, const char __user *u, size_t count,
 		struct plock_xop *xop;
 		xop = (struct plock_xop *)op;
 		if (xop->callback)
-			count = dlm_plock_callback(op);
+			dlm_plock_callback(op);
 		else
 			wake_up(&recv_wq);
 	} else