gpio: gpio-74x164: Remove redundant spi_set_drvdata

Driver core sets driver data to NULL upon failure or remove.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>