remoteproc: stm32: improve debug using dev_err_probe

When possible use dev_err_probe help to properly deal with the
PROBE_DEFER error.
The benefit is that DEFER issue will be logged in the devices_deferred
debugfs file.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss-st.com>
Link: https://lore.kernel.org/r/20201217144125.12903-1-arnaud.pouliquen@foss.st.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>