ima: Remove ima_policy file before directory

commit f7333b95 upstream.

The removal of ima_dir currently fails since ima_policy still exists, so
remove the ima_policy file before removing the directory.

Fixes: 4af4662f

 ("integrity: IMA policy")
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Cc: <stable@vger.kernel.org>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>