drm/radeon/dpm/rs780: don't enable sclk scaling if not required

If the low and high sclks are the same, there is no need to
enable sclk scaling.  This causes display stability issues on
certain boards.

Fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=60857Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: NChristian König <christian.koenig@amd.com>

drivers/gpu/drm/radeon/rs780_dpm.c

@@ -499,6 +499,9 @@ static void rs780_activate_engine_clk_scaling(struct radeon_device *rdev,
 	    (new_state->sclk_low == old_state->sclk_low))
 		return;
 
+	if (new_state->sclk_high == new_state->sclk_low)
+		return;
+
 	rs780_clk_scaling_enable(rdev, true);
 }