gpio: remove use of __devexit

CONFIG_HOTPLUG is going away as an option so __devexit is no
longer needed.

Signed-off-by: Bill Pemberton <wfp5p@virginia.edu>
Cc: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Peter Tyser <ptyser@xes-inc.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>