Fix compilation warning:
drivers/pinctrl/bcm/pinctrl-bcm4908.c: In function 'bcm4908_pinctrl_probe':
drivers/pinctrl/bcm/pinctrl-bcm4908.c:541:53: error: passing argument 3 of 'pinmux_generic_add_function' discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
541 | function->groups,
| ~~~~~~~~^~~~~~~~
In file included from drivers/pinctrl/bcm/pinctrl-bcm4908.c:16:
drivers/pinctrl/bcm/../pinmux.h:153:46: note: expected 'const char **' but argument is of type 'const char * const*'
153 | const char **groups,
| ~~~~~~~~~~~~~^~~~~~
cc1: all warnings being treated as errors
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>