dt-bindings: pinctrl: correct typo of description for cv1800

dt-bindings: pinctrl: correct typo of description for cv1800

It should be PINMUX/PINMUX2, not GPIOMUX/GPIOMUX2, see
<dt-bindings/pinctrl/pinctrl-cv1800b.h>.

Fixes: 64aa494de6fa ("dt-bindings: pinctrl: Add pinctrl for Sophgo CV1800 series SoC.")
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
Reviewed-by: Inochi Amaoto <inochiama@gmail.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/20241029012312.3448287-1-unicornxw@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>