cxd2820r: fix gpio null pointer dereference

cxd2820r: fix gpio null pointer dereference

BugLink: http://bugs.launchpad.net/bugs/1672544
commit 0ffb94b6cc5df6376ab6bff5b80075641f6716f8 upstream.

Setting GPIOs during probe causes null pointer deference when
GPIOLIB was not selected by Kconfig. Initialize driver private
field before calling set gpios.

It is regressing bug since 4.9.

Fixes: 07fdf7d9f19f ("[media] cxd2820r: add I2C driver bindings")
Reported-by: Chris Rankin <rankincj@gmail.com>
Tested-by: Chris Rankin <rankincj@gmail.com>
Tested-by: Håkan Lennestål <hakan.lennestal@gmail.com>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>