Fix static kernel build with options ZFS

This was broken by r271802.

MFC after:	1 week
X-MFC-With:	r271802
Sponsored by:	Multiplay


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271873 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f