Fix the benchmarks of pallet saft-registry

[clearloop]

Self::nav() broken, because no available assets yet,

For could not add_saft, the reason is like the issue in

PINT/pallets/asset-index/src/tests.rs

Line 115 in 810ea66

fn can_add_saft() {

, add another liquid asset will be able to fix it

Originally posted by @clearloop in #317 (comment)

Might need to add something like create_feed in #300 provided

[Redoudou]

Hey team! Please add your planning poker estimate with ZenHub @clearloop @mattsse