greybus: gpio: make gb_gpio_controller pointer naming consistent

Rename all struct gb_gpio_controller-pointer variables "ggc" for
consistency and readability reason.

This also fixes a bunch of lines that exceeded the 80 columns limit.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>