drm/vc4: dpi: Fix format mapping for RGB565

The mapping is incorrect for RGB565_1X16 as it should be
DPI_FORMAT_18BIT_666_RGB_1 instead of DPI_FORMAT_18BIT_666_RGB_3.

Fixes: 08302c35 ("drm/vc4: Add DPI driver")
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20221013-rpi-dpi-improvements-v3-7-eb76e26a772d@cerno.tech


Signed-off-by: Maxime Ripard <maxime@cerno.tech>