staging: line6: change monitor_level type ValueWait -> int

The monitor_level sysfs attr has been dropped and we never need to wait
on the monitor_level value to change.  Switch to a plain int and drop
the wait queue.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>