Fix select_asset can't be used in HPVestsAmountInput

This issue was observed in !487 (comment 185895)

Because CurrencySelectorBase previously used string to determine selection and in the AssetAmmountInput there was asset type required.

This caused a situation where Asset.Hive given for HPVestsAmountInput resulted in error because it was then converted to "HIVE" which can't be found in selectable (there is "HP" instead). Using type for selection solves this problem.