gpio: nomadik: fix offset bug in nmk_pmx_set()

gpio: nomadik: fix offset bug in nmk_pmx_set()

Previously, the statement looked like:

    slpm[x] &= ~BIT(g->grp.pins[i]);

Where:
 - slpm is a unsigned int pointer;
 - g->grp.pins[i] is a pin number. It can grow to more than 32.

The expected shift amount is a pin bank offset.

This bug does not occur on every group or pin: the altsetting must be
NMK_GPIO_ALT_C and the pin must be 32 or above. It might have occured.
For example, in pinctrl-nomadik-db8500.c, pin group i2c3_c_2 has the
right altsetting and pins 229 and 230.

Fixes: dbfe8ca259e1 ("pinctrl/nomadik: implement pin multiplexing")
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Link: https://lore.kernel.org/r/20240228-mbly-gpio-v2-5-3ba757474006@bootlin.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>