staging: usbip: userspace: fix build breakage in doc directory

File doc/usbip_bind_driver.8 does not exist any more but it is
listed in dist_man_MANS. This breaks the build of the userspace.
Remove the file from the list.

Signed-off-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Acked-by: David Chang <dchang@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>