Add a missing inline to the caching allocator accessor.
Add a missing inline to the caching allocator accessor.

Closes #1149.

Reviewed-by: David Olsen <c006f74ad218cd79aa222eb0f74d6fabc2b85975@nvidia.com>
Reviewed-by: Bryce Adelstein Lelbach aka wash <2f0f95f95a80179c2180af4c82f6ea311b6bd2c8@gmail.com>

andrewcorrigan/thrust-multi-permutation-iterator,thrust/thrust,jaredhoberock/thrust,thrust/thrust,andrewcorrigan/thrust-multi-permutation-iterator,jaredhoberock/thrust,andrewcorrigan/thrust-multi-permutation-iterator,thrust/thrust,thrust/thrust,jaredhoberock/thrust,jaredhoberock/thrust,thrust/thrust,jaredhoberock/thrust