staging: visorbus, replace init_timer with setup_timer

Newer version is more readable and needs less changes if/when
timer_struct is to be changed.

Signed-off-by: Stefan Svinciak <xsvinc1@fi.muni.cz>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: David Kershner <david.kershner@unisys.com>
Cc: <sparmaintainer@unisys.com>
Acked-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>