drm/i915: Prevent double dpms on

drm/i915: Prevent double dpms on

commit 032d2a0d068b0368296a56469761394ef03207c3 upstream.

Arguably this is a bug in drm-core in that we should not be called twice
in succession with DPMS_ON, however this is still occuring and we see
FDI link training failures on the second call leading to the occassional
blank display. For the time being ignore the repeated call.

Original patch by Dave Airlie <airlied@redhat.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>