sfxge: fix name conflict with crc32_table from sys/crc32.h

The header is not present on FreeBSD, but exists on OmniOS where sfxge
common code is used as well.

Reviewed by: gnn
Sponsored by: Solarflare Communications, Inc.
MFC after: 2 days
Differential Revision: https://reviews.freebsd.org/D4390