USB: WUSBCORE: Use usb_init_urb instead of creating the URB manually

In wa_seg_init, use usb_init_urb to init the URB object contained in the
transfer segment instead of initializing it manually.  Use kmalloc to
allocate the memory for segment instead of kzalloc and then use memset
to set the non-URB portion of the transfer segment struct to 0 since
that was already done by usb_init_urb.

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