zfs-dkms rpm: Fix scriptlets dependencies

To ensure that the necessary packages are available during the %post and
%preun scriptlets, require them properly.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Till Maas <opensource@till.name>
Closes #12822
Closes #12832