remoteproc: imx_rproc: Re-use existing error handling path in 'imx_rproc_probe()'

Avoid some code ducplication and be more future-proof.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>