tools: usb: testusb: change the help text

The 'length' is the transfer length, not the packet size, so
change the help text.

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
1 file changed