drm/radeon: add header comment for clarification to vce_v2_0_enable_mgcg()

Add function header comment to make it clear that local variable sw_cg
is used for debugging and it should not be removed.

Addresses-Coverity-ID: 1198635
Cc: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/vce_v2_0.c

@@ -104,6 +104,10 @@ static void vce_v2_0_disable_cg(struct radeon_device *rdev)
 	WREG32(VCE_CGTT_CLK_OVERRIDE, 7);
 }
 
+/*
+ * Local variable sw_cg is used for debugging purposes, in case we
+ * ran into problems with dynamic clock gating. Don't remove it.
+ */
 void vce_v2_0_enable_mgcg(struct radeon_device *rdev, bool enable)
 {
 	bool sw_cg = false;