doc: usb: gadget-testing: using the updated testusb.c
doc: usb: gadget-testing: using the updated testusb.c

testusb.c at http://www.linux-usb.org/usbtest/ is out of date,
using the one at the kernel source folder.

Cc: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org>
Signed-off-by: Peter Chen <c01a8c815a4ad165fff2d1c0d35ddf5b16bd3d7b@freescale.com>
Signed-off-by: Felipe Balbi <94dddeeef08b001e003cce128ddc162a4e2c6cd2@ti.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs