drm/amd/powerplay/smu7_hwmgr: 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>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/powerplay/hwmgr/smu7_hwmgr.c

@@ -3681,10 +3681,12 @@ static int smu7_request_link_speed_change_before_state_change(
 			data->force_pcie_gen = PP_PCIEGen2;
 			if (current_link_speed == PP_PCIEGen2)
 				break;
+			/* fall through */
 		case PP_PCIEGen2:
 			if (0 == amdgpu_acpi_pcie_performance_request(hwmgr->adev, PCIE_PERF_REQ_GEN2, false))
 				break;
 #endif
+			/* fall through */
 		default:
 			data->force_pcie_gen = smu7_get_current_pcie_speed(hwmgr);
 			break;