gdb/testsuite: update field names in gdb-gdb.py.in

Patches that renamed the type::length and type::target_type fields
didn't update gdb-gdb.py.in accordingly, do that.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29599
Change-Id: I0f3f37a94d43497789156b0ded4d2f2dd5b89496
1 file changed