Recursive hackage import fails

Importing hackage packages recursively fails with similar error to this:

```

$ guix import hackage linear-generics --recursive

Backtrace:

11 (primitive-load "/home/saku/.config/guix/current/bin/gu…")

In guix/ui.scm:

2309:7 10 (run-guix . _)

2272:10 9 (run-guix-command _ . _)

In guix/scripts/import.scm:

90:11 8 (guix-import . _)

In guix/scripts/import/hackage.scm:

129:26 7 (guix-import-hackage . _)

In guix/import/utils.scm:

651:3 6 (recursive-import _ #:repo->guix-package _ #:guix-name . #)

613:31 5 (topological-sort _ #<procedure 7f8f515f4720 at guix/i…> …)

655:29 4 (_ _)

In unknown file:

3 (remove #<procedure 7f8f51610ce0 at guix/import/utils.…> …)

In guix/import/utils.scm:

635:39 2 (exists? #<<upstream-input> name: "th-abstraction" dow…> …)

In guix/import/hackage.scm:

128:6 1 (hackage-name->package-name #<<upstream-input> name: "t…>)

In unknown file:

0 (string-prefix? "ghc-" #<<upstream-input> name: "th-ab…> …)

ERROR: In procedure string-prefix?:

In procedure string-prefix?: Wrong type argument in position 2 (expecting string): #<<upstream-input> name: "th-abstraction" downstream-name: "ghc-th-abstraction" type: regular min-version: any max-version: any>

```

I tried to find out what passes the `upstream-input` to

`hackage-name->package-name`, but only found out with `pk` that it seems

to only happen with the recursed dependencies and not with the root

package. I also tried to make `hackage-name->package-name` accept

`upstream-input` records but that a new error, so I assume the issue is

that something in the importer is returning `upstream-input` records

when it should return package names.

I could try to debug this further but I don't feel like I know enough

about debugging with guile nor about debugging scheme.