staging: mt7621-dts: avoid warnings in pinctrl definitions
The device-tree checking code sees node names "i2c" and "spi" in the
pinctrl definition and thinks these are defining i2c or spi devices,
and complains that they look wrong.
So add a '0' to the end of each name (much like "uart" and "rgmii"
have numbers at the end) to avoid the warning.