pinctrl: meson: pinctrl-meson-a1: Remove unused const variable 'i2c_slave_groups'

It has never been used.

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

 drivers/pinctrl/meson/pinctrl-meson-a1.c:749:27: warning: ‘i2c_slave_groups’ defined but not used [-Wunused-const-variable=]
 749 | static const char const i2c_slave_groups[] = {
 | ^~~~~~~~~~~~~~~~
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: Qianggui Song <qianggui.song@amlogic.com>
Cc: linux-amlogic@lists.infradead.org
Link: https://lore.kernel.org/r/20200713144930.1034632-24-lee.jones@linaro.orgSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/meson/pinctrl-meson-a1.c

@@ -746,11 +746,6 @@ static const char * const i2c3_groups[] = {
 	"i2c3_sck_x", "i2c3_sda_x", "i2c3_sck_f", "i2c3_sda_f",
 };
 
-static const char * const i2c_slave_groups[] = {
-	"i2c_slave_sda_a", "i2c_slave_sck_a",
-	"i2c_slave_sda_f", "i2c_slave_sck_f",
-};
-
 static const char * const spi_a_groups[] = {
 	"spi_a_mosi_x2", "spi_a_ss0_x3", "spi_a_sclk_x4", "spi_a_miso_x5",
 	"spi_a_mosi_x7", "spi_a_miso_x8", "spi_a_ss0_x9", "spi_a_sclk_x10",