drm/amd/display: Mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch
cases where we are expecting to fall through.

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enable -Wimplicit-fallthrough.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_dccg.c

@@ -102,14 +102,19 @@ void dccg2_init(struct dccg *dccg)
 	switch (dccg_dcn->base.ctx->dc->res_pool->pipe_count) {
 	case 6:
 		REG_UPDATE(DPPCLK_DTO_CTRL, DPPCLK_DTO_DB_EN[5], 1);
+		/* Fall through */
 	case 5:
 		REG_UPDATE(DPPCLK_DTO_CTRL, DPPCLK_DTO_DB_EN[4], 1);
+		/* Fall through */
 	case 4:
 		REG_UPDATE(DPPCLK_DTO_CTRL, DPPCLK_DTO_DB_EN[3], 1);
+		/* Fall through */
 	case 3:
 		REG_UPDATE(DPPCLK_DTO_CTRL, DPPCLK_DTO_DB_EN[2], 1);
+		/* Fall through */
 	case 2:
 		REG_UPDATE(DPPCLK_DTO_CTRL, DPPCLK_DTO_DB_EN[1], 1);
+		/* Fall through */
 	case 1:
 		REG_UPDATE(DPPCLK_DTO_CTRL, DPPCLK_DTO_DB_EN[0], 1);
 		break;