drm/radeon: fix cursor corruption on DCE6 and newer

Aruba and newer gpu does not need the avivo cursor work around,
quite the opposite this work around lead to corruption.

agd5f: check DCE6 rather than ARUBA since the issue is DCE
version specific rather than family specific.
Signed-off-by: NJerome Glisse <jglisse@redhat.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/radeon_cursor.c

@@ -241,7 +241,8 @@ int radeon_crtc_cursor_move(struct drm_crtc *crtc,
 		y = 0;
 	}
 
-	if (ASIC_IS_AVIVO(rdev)) {
+	/* fixed on DCE6 and newer */
+	if (ASIC_IS_AVIVO(rdev) && !ASIC_IS_DCE6(rdev)) {
 		int i = 0;
 		struct drm_crtc *crtc_p;