drm/radeon: avoid a useless memset

Avoid a memset after a call to 'dma_alloc_coherent()'.
This is useless since
commit 518a2f19 ("dma-mapping: zero memory returned from dma_alloc_*")
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_gart.c

@@ -85,7 +85,6 @@ int radeon_gart_table_ram_alloc(struct radeon_device *rdev)
 	}
 #endif
 	rdev->gart.ptr = ptr;
-	memset((void *)rdev->gart.ptr, 0, rdev->gart.table_size);
 	return 0;
 }