USB: core: fix up kerneldoc comment

Make the kerneldoc comment for usb_find_common_endpoints_reverse()
self-contained by adding a full description and removing the reference
to usb_find_common_endpoints().

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>