drm/amd/amdgpu/amdgpu_ttm: Fix incorrectly documented function 'amdgpu_ttm_copy_mem_to_mem()'

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c:311: warning: expecting prototype for amdgpu_copy_ttm_mem_to_mem(). Prototype was for amdgpu_ttm_copy_mem_to_mem() instead

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Jerome Glisse <glisse@freedesktop.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -294,7 +294,7 @@ static int amdgpu_ttm_map_buffer(struct ttm_buffer_object *bo,
 }
 
 /**
- * amdgpu_copy_ttm_mem_to_mem - Helper function for copy
+ * amdgpu_ttm_copy_mem_to_mem - Helper function for copy
  * @adev: amdgpu device
  * @src: buffer/address where to read from
  * @dst: buffer/address where to write to