Fix #571 libPMacc limits: 32 bit host

Fix for #571: on 32bit hosts, size_t is the same as uint32_t (hopefully) which declares the `max` for it twice.

Reported by @sigkill on github, thanks!

@psychocoderHPC @f-schmitt-zih can one of you please review that? :)

- [x] @ax3l needs to be cherry-picked in `release-beta-rc6` afterwards
OK. Then leave it as it is.