mmc: owl: fix deferred probing

The driver overrides the error codes returned by platform_get_irq() to
-EINVAL, so if it returns -EPROBE_DEFER, the driver will fail the probe
permanently instead of the deferred probing. Switch to propagating the
error codes upstream.

Fixes: ff65ffe4

 ("mmc: Add Actions Semi Owl SoCs SD/MMC driver")
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Link: https://lore.kernel.org/r/20230617203622.6812-8-s.shtylyov@omp.ru
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>