usb: storage: onetouch: tighten a range check

Smatch complains because we only allocate ONETOUCH_PKT_LEN (2) bytes
but later when we call usb_fill_int_urb() we assume maxp can be up
to 8 bytes.  I talked to the maintainer and maxp should be capped at
ONETOUCH_PKT_LEN.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>