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 <[e-mail]>
Reviewed-by: Inochi Amaoto <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

Documentation/devicetree/bindings/pinctrl/sophgo,cv1800-pinctrl.yaml

···
           pinmux:
             description: |
               The list of GPIOs and their mux settings that properties in the
-              node apply to. This should be set using the GPIOMUX or GPIOMUX2
+              node apply to. This should be set using the PINMUX or PINMUX2
               macro.
 
           bias-pull-up: