usb: wusbcore: adjust iterator correctly when searching for ep comp descriptor

If the endpoint companion descriptor is not the first descriptor in the
extra descriptor buffer of a usb_host_endpoint, the loop in
rpipe_epc_find will get its buffer pointer and remaining size values out
of sync.  The buffer ptr 'itr' is advanced by the descriptor's bLength
field but the remaining size value 'itr_size' is decremented by the
bDescriptorType field which is incorrect.  This patch fixes the loop to
decrement itr_size by bLength as it should.

Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>