Add dev_warn_probe() and improve error handling in

Merge series from Dragan Simic <dsimic@manjaro.org>:

This is a small series that introduces dev_warn_probe() function, which
produces warnings on failed resource acquisitions, and improves error
handling in the probe paths of Rockchip SPI drivers, by using functions
dev_err_probe() and dev_warn_probe() properly in multiple places.

This series also performs a bunch of small, rather trivial code cleanups,
to make the code neater and a bit easier to read.