pinctrl: renesas: Remove unused pfc parameter from .pin_to_pocctrl()

The pfc parameter of the .pin_to_pocctrl() method was never used.
It is a relic of the old I/O voltage handling before commit
8775306d

 ("pinctrl: sh-pfc: refactor voltage setting").

Remove the parameter, as it prevents the checker from calling this
function for validating consistency of the pin control tables.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/822133086f32618c7fc920123c6a96f5d4ea7ad6.1640270559.git.geert+renesas@glider.be