media: solo6x10: hide unused variable

media: solo6x10: hide unused variable

When building without CONFIG_GPIOLIB, we get a harmless
warning about an unused variable:

drivers/media/pci/solo6x10/solo6x10-gpio.c: In function 'solo_gpio_init':
drivers/media/pci/solo6x10/solo6x10-gpio.c:165:6: error: unused variable 'ret' [-Werror=unused-variable]

This adds another #ifdef around the declaration.

Fixes: d3202d1981dc ("media: solo6x10: export hardware GPIO pins 8:31 to gpiolib interface")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ismael Luceno <ismael@iodev.co.uk>
Acked-by: Anton Sviridenko <anton@corp.bluecherry.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>