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.

Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>