pinctrl: pinmux: Add some missing parameter descriptions

pinctrl: pinmux: Add some missing parameter descriptions

And rename another which has probably bitrotted.

Fixes the following W=1 kernel build warning(s):

 drivers/pinctrl/pinmux.c:83: warning: Function parameter or member 'pctldev' not described in 'pinmux_can_be_used_for_gpio'
 drivers/pinctrl/pinmux.c:108: warning: Function parameter or member 'pctldev' not described in 'pin_request'
 drivers/pinctrl/pinmux.c:261: warning: Function parameter or member 'gpio' not described in 'pinmux_request_gpio'
 drivers/pinctrl/pinmux.c:751: warning: Function parameter or member 'selector' not described in 'pinmux_generic_get_function'
 drivers/pinctrl/pinmux.c:751: warning: Excess function parameter 'group_selector' description in 'pinmux_generic_get_function'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200713144930.1034632-13-lee.jones@linaro.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>