libsa: smbios: style(9): SMBIOS_GET8(): Split overlong line

No functional change.

Reviewed by: markj
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D49279

(cherry picked from commit 085c8bdec5bcb01acff5c6e9cd2d8864f44a20cd)