Block dimension validation is comparing in the wrong direction

[eyalroz]

As noted in #545 , when validation is performed fully, we get an error for valid block sizes, e.g. 32, as supposedly being too large. This is due to a wrong direction of comparison in the check() lambda within cuda::detail_::validate_block_dimension_compatibility(). Let's fix that. Or rather, we already have, and let's mark it fixed.