We need to handle mmc_of_parse() errors during probe.

This finally fixes the wifi regression on Raspberry Pi 3 series.
In error case the wifi chip was permanently in reset because of
the power sequence depending on the deferred probe of the GPIO expander.

Fixes: b580c52d ("mmc: sdhci-iproc: add IPROC SDHCI driver")
Cc: stable@vger.kernel.org
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>