drm/amdgpu/display: add fallthrough comment

To avoid a compiler warning.

Reviewed-by: Zhan Liu <zhan.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dce/dce_aux.c

@@ -617,6 +617,7 @@ bool dce_aux_transfer_with_retries(struct ddc_service *ddc,
 			case AUX_TRANSACTION_REPLY_AUX_DEFER:
 			case AUX_TRANSACTION_REPLY_I2C_OVER_AUX_DEFER:
 				retry_on_defer = true;
+				/* fall through */
 			case AUX_TRANSACTION_REPLY_I2C_OVER_AUX_NACK:
 				if (++aux_defer_retries >= AUX_MAX_DEFER_RETRIES) {
 					goto fail;