drm/amdgpu/si/dpm: fix phase shedding setup

Used the wrong index to setup the phase shedding mask.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/amd/amdgpu/sislands_smc.h b/drivers/gpu/drm/amd/amdgpu/sislands_smc.h
index ee4b846..d2930ec 100644
--- a/drivers/gpu/drm/amd/amdgpu/sislands_smc.h
+++ b/drivers/gpu/drm/amd/amdgpu/sislands_smc.h
@@ -194,6 +194,7 @@
 #define SISLANDS_SMC_VOLTAGEMASK_VDDC  0
 #define SISLANDS_SMC_VOLTAGEMASK_MVDD  1
 #define SISLANDS_SMC_VOLTAGEMASK_VDDCI 2
+#define SISLANDS_SMC_VOLTAGEMASK_VDDC_PHASE_SHEDDING 3
 #define SISLANDS_SMC_VOLTAGEMASK_MAX   4
 
 struct SISLANDS_SMC_VOLTAGEMASKTABLE