arm64: dts: mediatek: mt7622: fix "emmc" pinctrl mux

arm64: dts: mediatek: mt7622: fix "emmc" pinctrl mux

Value "emmc_rst" is a group name and should be part of the "groups"
property.

This fixes:
arch/arm64/boot/dts/mediatek/mt7622-rfb1.dtb: pinctrl@10211000: emmc-pins-default:mux:function: ['emmc', 'emmc_rst'] is too long
        from schema $id: http://devicetree.org/schemas/pinctrl/mediatek,mt7622-pinctrl.yaml#
arch/arm64/boot/dts/mediatek/mt7622-bananapi-bpi-r64.dtb: pinctrl@10211000: emmc-pins-default:mux:function: ['emmc', 'emmc_rst'] is too long
        from schema $id: http://devicetree.org/schemas/pinctrl/mediatek,mt7622-pinctrl.yaml#

Fixes: 3725ba3f5574 ("arm64: dts: mt7622: add pinctrl related device nodes")
Fixes: 0b6286dd96c0 ("arm64: dts: mt7622: add bananapi BPI-R64 board")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20240604074916.7929-1-zajec5@gmail.com
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>