pinctrl: pinctrl-single: Fix pcs_request_gpio() when bits_per_mux != 0

pinctrl: pinctrl-single: Fix pcs_request_gpio() when bits_per_mux != 0

This fixes pcs_request_gpio() in the pinctrl-single driver when
bits_per_mux != 0. It appears this was overlooked when the multiple
pins per register feature was added.

Fixes: 4e7e8017a80e ("pinctrl: pinctrl-single: enhance to configure multiple pins of different modules")
Signed-off-by: David Lechner <david@lechnology.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>