drm/amdgpu: Remove redundant NULL check

Fix below warnings reported by coccicheck:
./drivers/gpu/drm/amd/display/dc/clk_mgr/dcn30/dcn30_clk_mgr.c:557:2-7: WARNING: NULL check before some freeing functions is not needed.

Fixes: 4d55b0dd ("drm/amd/display: Add DCN3 CLK_MGR")
Signed-off-by: Li Heng <liheng40@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/clk_mgr/dcn30/dcn30_clk_mgr.c

@@ -553,8 +553,7 @@ void dcn3_clk_mgr_construct(
 
 void dcn3_clk_mgr_destroy(struct clk_mgr_internal *clk_mgr)
 {
-	if (clk_mgr->base.bw_params)
-		kfree(clk_mgr->base.bw_params);
+	kfree(clk_mgr->base.bw_params);
 
 	if (clk_mgr->wm_range_table)
 		dm_helpers_free_gpu_mem(clk_mgr->base.ctx, DC_MEM_ALLOC_TYPE_GART,