remoteproc: stm32: Clean up redundant dev_err_probe()

remoteproc: stm32: Clean up redundant dev_err_probe()

Referring to platform_get_irq()'s definition, the return value has
already been checked if ret < 0, and printed via dev_err_probe().
Calling dev_err_probe() one more time outside platform_get_irq()
is obviously redundant. Removing outside dev_err_probe() to
clean it up.

Besides, switch to use platform_get_irq_optional() since the irq
is optional here.

Signed-off-by: Chen Jiahao <chenjiahao16@huawei.com>
Acked-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20230817083336.404635-1-chenjiahao16@huawei.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>