Fix parsable 'zfs get' for compressratios

This is consistent with the change introduced in bc2d809 where
'zpool get -p dedupratio' does not add a trailing "x" to the output.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #6436
Closes #6449