ovl: fix get_acl() on tmpfs

tmpfs doesn't have ->get_acl() because it only uses cached acls.

This fixes the acl tests in pjdfstest when tmpfs is used as the upper layer
of the overlay.
Reported-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 39a25b2b ("ovl: define ->get_acl() for overlay inodes")
Cc: <stable@vger.kernel.org> # v4.8

fs/overlayfs/inode.c

@@ -270,9 +270,6 @@ struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 	if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
 		return NULL;
 
-	if (!realinode->i_op->get_acl)
-		return NULL;
-
 	old_cred = ovl_override_creds(inode->i_sb);
 	acl = get_acl(realinode, type);
 	revert_creds(old_cred);