[GFS2] Fix OOM error handling

Fix the OOM error handling in inode.c where it was possible for
a NULL pointer to be dereferenced.

Signed-off-by: Steven Whitehouse <[e-mail]>

fs/gfs2/inode.c

···
 	struct gfs2_glock *io_gl;
 	int error;
 
+	if (!inode)
+		return ERR_PTR(-ENOBUFS);
+
 	if (inode->i_state & I_NEW) {
 		struct gfs2_sbd *sdp = GFS2_SB(inode);
 		umode_t mode = DT2IF(type);