pinctrl: meson-axg: add missing GPIOA_18 gpio group

Without this, the gpio cannot be explicitly mux'ed to its gpio function.

Fixes: 83c566806a68a ("pinctrl: meson-axg: Add new pinctrl driver for Meson AXG SoC")
Cc: [e-mail]
Signed-off-by: Martin Hundebøll <[e-mail]>
Reviewed-by: Neil Armstrong <[e-mail]>
Reviewed-by: Dmitry Rokosov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/meson/pinctrl-meson-axg.c

···
 	GPIO_GROUP(GPIOA_15),
 	GPIO_GROUP(GPIOA_16),
 	GPIO_GROUP(GPIOA_17),
+	GPIO_GROUP(GPIOA_18),
 	GPIO_GROUP(GPIOA_19),
 	GPIO_GROUP(GPIOA_20),