kaweth: fix firmware download

commit 60bcabd0 upstream.

This fixes the oops discovered by the Umap2 project and Alan Stern.
The intf member needs to be set before the firmware is downloaded.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>