pinctrl: actions: Fix uninitialized error in owl_pin_config_set()

With gcc 4.1.2:

    drivers/pinctrl/actions/pinctrl-owl.c: In function ‘owl_pin_config_set’:
    drivers/pinctrl/actions/pinctrl-owl.c:336: warning: ‘ret’ may be used uninitialized in this function

Indeed, if num_configs is zero, the uninitialized value will be returned
as an error code.

Fix this by preinitializing it to zero.

Fixes: 2242ddfb ("pinctrl: actions: Add Actions S900 pinctrl driver")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>