USB: serial: iuu_phoenix: fix NULL-deref at open

commit 90507d54f712d81b74815ef3a4bbb555cd9fab2f upstream.

Fix NULL-pointer dereference at open should the device lack a bulk-in or
bulk-out endpoint:

Unable to handle kernel NULL pointer dereference at virtual address 00000030
...
PC is at iuu_open+0x78/0x59c [iuu_phoenix]

Fixes: 07c3b1a1 ("USB: remove broken usb-serial num_endpoints
check")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>