Update app/icahost.go

Signed-off-by: yihuang <huang@crypto.com>

app/icahost.go

@@ -7,6 +7,8 @@ import (
  icatypes "github.com/cosmos/ibc-go/v8/modules/apps/27-interchain-accounts/types"
 )
 
+// ICAHostMockSubspace is a mock implementation to workaround the migration process, because we have nothing to migrate from,
+otherwise it'll panic, see: https://github.com/cosmos/ibc-go/pull/6167
 type ICAHostMockSubspace struct {
 }