dump-guest-memory.py: fix No symbol "vmcoreinfo_find"

dump-guest-memory.py: fix No symbol "vmcoreinfo_find"

When qemu is compiled without debug, the dump gdb python script can fail with:

Error occurred in Python command: No symbol "vmcoreinfo_find" in current context.

Because vmcoreinfo_find() is inlined and not exported.

Use the underlying object_resolve_path_type() to get the instance instead.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>