Name the Pin Function Controller subnode for VIN1 after its device name,
instead of using the generic and indexless "vin".

This avoids conflicts when enabling support for more video inputs 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>