drm/i915/ttm: fix sparse warning

Sparse complains with:

drivers/gpu/drm/i915/gem/i915_gem_ttm.c:1066:21: sparse:
	expected restricted vm_fault_t [assigned] [usertype] ret
drivers/gpu/drm/i915/gem/i915_gem_ttm.c:1066:21: sparse: got int

Fixes: 516198d3

 ("drm/i915: audit bo->resource usage v3")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230130101230.25347-1-matthew.auld@intel.com
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Acked-by: Christian König <ckoenig.leichtzumerken@gmail.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
(cherry picked from commit fde789e8

)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>