usb: wusbcore: fix below build warning

linux-2.6/drivers/usb/wusbcore/wa-xfer.c: In function 'wa_buf_in_cb':
linux-2.6/drivers/usb/wusbcore/wa-xfer.c:2590: warning: 'rpipe' may be used uninitialized in this function

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Suggested-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>