gpio: omap: prevent module from being unloaded while in use

OMAP GPIO driver allowed to be built as loadable module, but it
doesn't set owner field in GPIO chip structure. As result,
module_get/put() API is not working and it's possible to unload
OMAP driver while in use:

  omap_gpio 48051000.gpio: REMOVING GPIOCHIP WITH GPIOS STILL REQUESTED

Hence, add missing configuration.

Cc: Tony Lindgren <tony@atomide.com>
Fixes: cac089f9 ('gpio: omap: Allow building as a loadable module')
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>