drm/amdgpu: use kmemdup rather than duplicating its implementation

The patch was generated using fixed coccinelle semantic patch
scripts/coccinelle/api/memdup.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2014320Signed-off-by: NAndrzej Hajda <a.hajda@samsung.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_object.c

@@ -536,12 +536,10 @@ int amdgpu_bo_set_metadata (struct amdgpu_bo *bo, void *metadata,
 	if (metadata == NULL)
 		return -EINVAL;
 
-	buffer = kzalloc(metadata_size, GFP_KERNEL);
+	buffer = kmemdup(metadata, metadata_size, GFP_KERNEL);
 	if (buffer == NULL)
 		return -ENOMEM;
 
-	memcpy(buffer, metadata, metadata_size);
-
 	kfree(bo->metadata);
 	bo->metadata_flags = flags;
 	bo->metadata = buffer;