remoteproc: imx_rproc: Simplify some error message

dev_err_probe() already prints the error code in a human readable way, so
there is no need to duplicate it as a numerical value at the end of the
message.

While at it, remove 'ret' that is mostly useless.

Fixes: 2df70620 ("remoteproc: imx_proc: enable virtio/mailbox")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/6b9343c2688117a340661d8ee491c2962c54a09a.1659736936.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>