drm/dp_mst: Combine redundant cases in drm_dp_encode_sideband_req()

Noticed this while working on adding a drm_dp_decode_sideband_req().
DP_POWER_DOWN_PHY/DP_POWER_UP_PHY both use the same struct as
DP_ENUM_PATH_RESOURCES, so we can just combine their cases.

Changes since v2:
* Fix commit message
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Juston Li <juston.li@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <hwentlan@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190903215702.16984-1-lyude@redhat.com

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -271,6 +271,8 @@ static void drm_dp_encode_sideband_req(struct drm_dp_sideband_msg_req_body *req,
 
 	switch (req->req_type) {
 	case DP_ENUM_PATH_RESOURCES:
+	case DP_POWER_DOWN_PHY:
+	case DP_POWER_UP_PHY:
 		buf[idx] = (req->u.port_num.port_number & 0xf) << 4;
 		idx++;
 		break;
@@ -358,12 +360,6 @@ static void drm_dp_encode_sideband_req(struct drm_dp_sideband_msg_req_body *req,
 		memcpy(&buf[idx], req->u.i2c_write.bytes, req->u.i2c_write.num_bytes);
 		idx += req->u.i2c_write.num_bytes;
 		break;
-
-	case DP_POWER_DOWN_PHY:
-	case DP_POWER_UP_PHY:
-		buf[idx] = (req->u.port_num.port_number & 0xf) << 4;
-		idx++;
-		break;
 	}
 	raw->cur_len = idx;
 }