pinctrl: sh-pfc: r8a7791: SD1_CLK fix

Fix the SD1_CLK handling for r8a7791. Without this patch
it is impossible to request all pins needed for SDHI1 on
the Koelsch board.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>