drm/ttm: Fix 'buf' pointer update in ttm_bo_vm_access_kmap() (v2)

drm/ttm: Fix 'buf' pointer update in ttm_bo_vm_access_kmap() (v2)

commit 95244db2d3f743f37e69446a2807dd1a42750542 upstream.

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: 09ac4fcb3f25 ("drm/ttm: Implement vm_operations_struct.access v2")

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>