gpio-ich: Check for pin availability at request time

Stop checking for pin availability in direction and get functions.
These functions can be called repeatedly, so checking every time is
bad for performance. Now that requesting GPIO pins is no longer
optional, checking for availability at pin request time is enough.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Peter Tyser <ptyser@xes-inc.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>