USB: whci-hcd: check return value of usb_hcd_link_urb_to_ep()

Check the return value of usb_hcd_link_urb_to_ep() and do not add the
urb to the ASL/PZL if it returns an error.

Omitting the check results in urbs that appear to be submitted
successfully but then cannot be unliked (because
usb_hcd_check_unlink_urb() returns an error).  This can cause khubd (for
example) to block forever in usb_kill_urb().

Signed-off-by: David Vrabel <david.vrabel@csr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>