gpio: samsung: Remove remaining check for CONFIG_S5P_GPIO_DRVSTR

Commit d78c16cc ("ARM: SAMSUNG: Remove remaining legacy code")
removed the Kconfig symbol S5P_GPIO_DRVSTR. It didn't remove one check
for the related macro. Remove that check and the dead code it hides.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Reviewed-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>