The buf pointer was not being incremented inside the loop
meaning the same block of data would be read or written
repeatedly.

(v2) Change 'buf' pointer to uint8_t* type

Cc: stable@vger.kernel.org
Fixes: 09ac4fcb ("drm/ttm: Implement vm_operations_struct.access v2")
Signed-off-by: NTom St Denis <tom.stdenis@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>