zfs-kmod: fix empty rpm requires/conflicts

Fix an error in zfs-kmod.spec that causes kmod-zfs packages not to
include the correct RPM requires/conflicts relationships. With this
change applied, RPM correctly no longer allows kmod-zfs & zfs-dkms
packages to be installed together.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Todd Seidelmann <18294602+seidelma@users.noreply.github.com>
Closes #16121