usb: dwc3: meson-g12a: check return of dwc3_meson_g12a_usb_init

The dwc3_meson_g12a_usb_init function can return an error, check it.

Fixes: c9999337

 ("usb: dwc3: Add Amlogic G12A DWC3 glue")
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>