ARM: dts: kzm9g: Name serial port pfc subnode after device name

Name the Pin Function Controller subnode for SCIFA4 after its device
name, instead of after the serial port alias.

This avoids conflicts when adding support for more serial ports later,
either here or in a DT overlay.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>