drm/amdgpu/powerplay/vega10: handle error in getting pptable

Rather than just silently dropping it.  Also fixes a set but
unused variable warning.
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega10_hwmgr.c

@@ -3141,6 +3141,8 @@ static int vega10_get_pp_table_entry(struct pp_hwmgr *hwmgr,
 
 	result = vega10_get_powerplay_table_entry(hwmgr, entry_index, state,
 			vega10_get_pp_table_entry_callback_func);
+	if (result)
+		return result;
 
 	/*
 	 * This is the earliest time we have all the dependency table