xfs: fix spin_is_locked assert on uni-processor builds

Without SMP or preemption spin_is_locked always returns false,
so we can't do an assert with it.  Instead use assert_spin_locked,
which does the right thing on all builds.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>
Reported-by: Johannes Engel <jcnengel@googlemail.com>
Tested-by: Johannes Engel <jcnengel@googlemail.com>
Signed-off-by: Felix Blyakher <felixb@sgi.com>

fs/xfs/xfs_log.c

@@ -3180,7 +3180,7 @@ xlog_state_sync(xlog_t	  *log,
 STATIC void
 xlog_state_want_sync(xlog_t *log, xlog_in_core_t *iclog)
 {
-	ASSERT(spin_is_locked(&log->l_icloglock));
+	assert_spin_locked(&log->l_icloglock);
 
 	if (iclog->ic_state == XLOG_STATE_ACTIVE) {
 		xlog_state_switch_iclogs(log, iclog, 0);