drm/amdgpu: use drm_mode_vrefresh() rather than mode->vrefresh

This is a port of radeon commit:
3d2d98ee1af0cf6eebfbd6bff4c17d3601ac1284
drm/radeon: use drm_mode_vrefresh() rather than mode->vrefresh
to amdgpu.

Signed-off-by: Alex Deucher <[e-mail]>
Cc: [e-mail]

drivers/gpu/drm/amd/amdgpu/amdgpu_dpm.c

···
 		list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
 			amdgpu_crtc = to_amdgpu_crtc(crtc);
 			if (crtc->enabled && amdgpu_crtc->enabled && amdgpu_crtc->hw_mode.clock) {
-				vrefresh = amdgpu_crtc->hw_mode.vrefresh;
+				vrefresh = drm_mode_vrefresh(&amdgpu_crtc->hw_mode);
 				break;
 			}
 		}