pinctrl: renesas: Simplify multiplication/shift logic

"a * (1 << b)" == "a << b".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/31eaa3226c61ecf653e2b031307eea42a9a3d54e.1645460548.git.geert+renesas@glider.be