ZTS: Fix add-o_ashift.ksh

Use option '-o' after action for compatibility

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Igor Kozhukhov <igor@dilos.org>
Closes openzfs#10426

tests/zfs-tests/tests/functional/cli_root/zpool_add/add-o_ashift.ksh

@@ -75,7 +75,7 @@ typeset badvals=("off" "on" "1" "8" "17" "1b" "ff" "-")
 for badval in ${badvals[@]}
 do
 	log_must zpool create $TESTPOOL $disk1
-	log_mustnot zpool add $TESTPOOL -o ashift="$badval" $disk2
+	log_mustnot zpool add -o ashift="$badval" $TESTPOOL $disk2
 	# clean things for the next run
 	log_must zpool destroy $TESTPOOL
 	log_must zpool labelclear $disk1