The error path in probe attempts to put the device back into reset.
Should we fail to get the reset_gpio (such as a probe defer) we will
leave the error value in there, which the gpiod_set_value_cansleep on
the error path will attempt to deference.

Fix this issue by clearing reset_gpio before we head into the error
path.
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Brian Austin <brian.austin@cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>