usbredir: fix free call

usbredir: fix free call

data might point into the middle of a larger buffer, there is a separate
free_on_destroy pointer passed into bufp_alloc() to handle that.  It is
only used in the normal workflow though, not when dropping packets due
to the queue being full.  Fix that.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/491
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210722072756.647673-1-kraxel@redhat.com>