ideapad: read brightness setting on brightness key notify

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=25922



On ideapad Y530, the brightness key notify will be blocked if the last notify
is not responsed by getting the brightness value. Read value when we get the
notify shall fix the problem and will not have any difference on other ideapads.

Signed-off-by: Ike Panhc <ike.pan@canonical.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>