Fix inverted check for --enable-pyzfs

The --{en,dis}able-pyzfs check is backwards. Fix that.

Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Signed-off-by: DHE <git@dehacked.net>
Closes #7493