arm64: dts: rockchip: Add vcc-supply to SPI flash on rk3566-rock3c

arm64: dts: rockchip: Add vcc-supply to SPI flash on rk3566-rock3c

As described in the radxa_rock_3c_v1400_schematic.pdf, the SPI Flash's
VCC connector is connected to VCCIO_FLASH and according to the
that same schematic, that belongs to the VCC_1V8 power source.

This fixes the following warning:

  spi-nor spi4.0: supply vcc not found, using dummy regulator

Fixes: ee219017ddb5 ("arm64: dts: rockchip: Add Radxa ROCK 3C")
Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Link: https://lore.kernel.org/r/20250506195702.593044-1-pbrobinson@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>