Fix build of liquidio with base gcc on i386

Some casts from pointers to uint64_t and back in lio_main.c cause base
gcc on i386 to warn "cast from pointer to integer of different size",
and vice versa. Add additional casts to uintptr_t to suppress these.

Reviewed by: sbruno
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D15754