drm/amd/display: Check msg->size before starting aux transfer

This patch adds an essential check related to the size of the
payload to be transferred via aux channel.

Without this check dal_ddc_service_read_dpcd_data() is fed with
inappropriate payload size leading to deadlocks.
Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c

@@ -85,6 +85,9 @@ static ssize_t dm_dp_aux_transfer(struct drm_dp_aux *aux,
 	enum ddc_result res;
 	ssize_t read_bytes;
 
+	if (WARN_ON(msg->size > 16))
+		return -E2BIG;
+
 	switch (msg->request & ~DP_AUX_I2C_MOT) {
 	case DP_AUX_NATIVE_READ:
 		read_bytes = dal_ddc_service_read_dpcd_data(