staging: vme_user: rename USER_BUS_MAX to VME_USER_BUS_MAX

Signed-off-by: Manohar Vanga <manohar.vanga@cern.ch>
Cc: Martyn Welch <martyn.welch@ge.com>
Reviewed-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>