staging: unisys: visorinput: no need to track open count

evdev_open_device() and evdev_close_device() (in evdev.c) already track
the open count under lock, and will only call visorinput_open() on the
first open and visorinput_close() on the last close.  So this patch
removes the unnessary logic from visorinput, and the now-unused counter
from the struct.

Signed-off-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>