USB: iowarrior: fix NULL-deref at probe

commit b7321e81fc369abe353cf094d4f0dc2fe11ab95f upstream.

Make sure to check for the required interrupt-in endpoint to avoid
dereferencing a NULL-pointer should a malicious device lack such an
endpoint.

Note that a fairly recent change purported to fix this issue, but added
an insufficient test on the number of endpoints only, a test which can
now be removed.

Fixes: 4ec0ef3a ("USB: iowarrior: fix oops with malicious USB descriptors")
Fixes: 946b960d ("USB: add driver for iowarrior devices.")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>