gpio: em: Return early on error in em_gio_probe()

em_gio_probe() uses managed initializations for everything but creating
the IRQ domain.  Hence in most failure cases, no cleanup needs to be
performed at all.

Make this clearer for the casual reviewer by returning early, instead of
jumping to an out-of-sight label.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>