Fix libblkid ZFS detection when making new pools

zfsonlinux/zfs@1db7b9be75a225cedb3b7a60028ca5695e5b8346 should have
fixed this, but this particular string was overlooked.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2288