'priv->workqueue' is destroyed in the error handling path of the probe but
not in the remove function.

Add the missing call to release some resources.

Cc: stable <stable@vger.kernel.org>
Fixes: 2df70620 ("remoteproc: imx_proc: enable virtio/mailbox")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Tested-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/d28ca94a4031bd7297d47c2164e18885a5a6ec19.1634366546.git.christophe.jaillet@wanadoo.frSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>