gpio: clps711x: Add module alias to support module auto loading

commit 55fe14ab "GPIO: clps711x: Rewrite driver for using generic GPIO code"
allows this driver to be built as a module.
Thus add module alias to support module auto loading.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>