drm/vc4: Calculate bpc based on max_requested_bpc

This aligns vc4 with Intel, AMD and Synopsis drivers and fixes max bpc
connector property not working as expected on monitors with YCbCr 4:2:2
support but not deep color support.

max_bpc in connector state is clamped at max_bpc from display info and
the latter only takes deep color modes into account so it will always
be 8, even if the display can do 4:2:2 12-bit output.

Signed-off-by: Matthias Reichl <hias@horus.com>

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -2124,7 +2124,7 @@ vc4_hdmi_encoder_compute_config(const struct vc4_hdmi *vc4_hdmi,
 {
 	struct drm_device *dev = vc4_hdmi->connector.dev;
 	struct drm_connector_state *conn_state = &vc4_state->base;
-	unsigned int max_bpc = clamp_t(unsigned int, conn_state->max_bpc, 8, 12);
+	unsigned int max_bpc = clamp_t(unsigned int, conn_state->max_requested_bpc, 8, 12);
 	unsigned int bpc;
 	int ret;