pinctrl: meson: fix unused variable warning

pinctrl: meson: fix unused variable warning

The kernel test robot reported a warning as below:
>> drivers/pinctrl/meson/pinctrl-meson-s4.c:178:27: warning: unused variable 'tdm_sclk1_c_pins' [-Wunused-const-variable]
   static const unsigned int tdm_sclk1_c_pins[]            = { GPIOC_3 };

Fix it by adding missing description about this pins

Fixes: 775214d389c2 ("pinctrl: meson: add pinctrl driver support for Meson-S4 Soc")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Qianggui Song <qianggui.song@amlogic.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20220330023720.18238-1-qianggui.song@amlogic.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>