remoteproc: imx_rproc: Fix an error handling path in 'imx_rproc_probe()'

If 'of_device_get_match_data()' fails, we must undo the previous
'rproc_alloc()' call.

Fixes: a0ff4aa6 ("remoteproc: imx_rproc: add a NXP/Freescale imx_rproc driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>