pinctrl: uniphier: set pinctrl_desc owner in common probe function

The owner of the struct pinctrl_desc matches that of platform_driver.
Set it in the common probe function.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>