xfs: fix unused log variable in xfs_log_cover()

The log variable is only used in kernels with asserts enabled.
Remove it and open code the dereference to avoid unused variable
warnings.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/xfs_log.c

@@ -1108,12 +1108,11 @@ static int
 xfs_log_cover(
 	struct xfs_mount	*mp)
 {
-	struct xlog		*log = mp->m_log;
 	int			error = 0;
 	bool			need_covered;
 
-	ASSERT((xlog_cil_empty(log) && xlog_iclogs_empty(log) &&
-	        !xfs_ail_min_lsn(log->l_ailp)) ||
+	ASSERT((xlog_cil_empty(mp->m_log) && xlog_iclogs_empty(mp->m_log) &&
+	        !xfs_ail_min_lsn(mp->m_log->l_ailp)) ||
 	       XFS_FORCED_SHUTDOWN(mp));
 
 	if (!xfs_log_writable(mp))