ceph: ceph_mdsc_build_path() returns an ERR_PTR

ceph_mdsc_build_path() returns an ERR_PTR but this code is set up to
handle NULL returns.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/debugfs.c

@@ -171,6 +171,8 @@ static int mdsc_show(struct seq_file *s, void *p)
 		} else if (req->r_dentry) {
 			path = ceph_mdsc_build_path(req->r_dentry, &pathlen,
 						    &pathbase, 0);
+			if (IS_ERR(path))
+				path = NULL;
 			spin_lock(&req->r_dentry->d_lock);
 			seq_printf(s, " #%llx/%.*s (%s)",
 				   ceph_ino(req->r_dentry->d_parent->d_inode),
@@ -187,6 +189,8 @@ static int mdsc_show(struct seq_file *s, void *p)
 		if (req->r_old_dentry) {
 			path = ceph_mdsc_build_path(req->r_old_dentry, &pathlen,
 						    &pathbase, 0);
+			if (IS_ERR(path))
+				path = NULL;
 			spin_lock(&req->r_old_dentry->d_lock);
 			seq_printf(s, " #%llx/%.*s (%s)",
 			   ceph_ino(req->r_old_dentry->d_parent->d_inode),