drm/radeon: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix multiple
warnings by explicitly adding multiple fallthrough pseudo-keyword macros,
as replacement for /* fall through */ comments.

Notice that Clang doesn't recognize /* fall through */ comments as
implicit fall-through markings.

Link: https://github.com/KSPP/linux/issues/115Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/ci_dpm.c

@@ -4839,8 +4839,8 @@ static void ci_request_link_speed_change_before_state_change(struct radeon_devic
 		case RADEON_PCIE_GEN2:
 			if (radeon_acpi_pcie_performance_request(rdev, PCIE_PERF_REQ_PECI_GEN2, false) == 0)
 				break;
+			fallthrough;
 #endif
-			/* fall through */
 		default:
 			pi->force_pcie_gen = ci_get_current_pcie_speed(rdev);
 			break;

drivers/gpu/drm/radeon/r300.c

@@ -1162,6 +1162,7 @@ static int r300_packet0_check(struct radeon_cs_parser *p,
 		/* valid register only on RV530 */
 		if (p->rdev->family == CHIP_RV530)
 			break;
+		fallthrough;
 		/* fallthrough do not move */
 	default:
 		goto fail;

drivers/gpu/drm/radeon/si_dpm.c

@@ -5745,8 +5745,8 @@ static void si_request_link_speed_change_before_state_change(struct radeon_devic
 		case RADEON_PCIE_GEN2:
 			if (radeon_acpi_pcie_performance_request(rdev, PCIE_PERF_REQ_PECI_GEN2, false) == 0)
 				break;
+			fallthrough;
 #endif
-			/* fall through */
 		default:
 			si_pi->force_pcie_gen = si_get_current_pcie_speed(rdev);
 			break;