pinctrl: baytrail: Fix potential NULL pointer dereference

saved-context in byt_gpio_probe is allocated via devm_kcalloc and is
used without checking for NULL in later functions. This patch avoids
such a scenario.

Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>