pinctrl: ocelot: Fix alt mode for ocelot

In case the driver was trying to set an alternate mode for gpio
0 or 32 then the mode was not set correctly. The reason is that
there is computation error inside the function ocelot_pinmux_set_mux
because in this case it was trying to shift to left by -1.
Fix this by actually shifting the function bits and not the position.

Fixes: 4b36082e

 ("pinctrl: ocelot: fix pinmuxing for pins after 31")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Link: https://lore.kernel.org/r/20230206203720.1177718-1-horatiu.vultur@microchip.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>