drm/nouveau: do not touch a powered-down card

This fixes https://bugs.freedesktop.org/show_bug.cgi?id=34430, where
a process (upowerd) would cause 100% CPU usage simply by trying to check
whether there is anything connected to the VGA connector.

Signed-off-by: Robert Varga <nite@hq.sk>

diff -u a/drivers/gpu/drm/nouveau/nv50_display.c b/drivers/gpu/drm/nouveau/nv50_display.c
--- a/drivers/gpu/drm/nouveau/nv50_display.c	2013-05-27 14:47:21.320111385 +0200
+++ b/drivers/gpu/drm/nouveau/nv50_display.c	2013-05-27 17:53:18.590174600 +0200
@@ -1556,6 +1556,10 @@
 	int ret, or = nouveau_encoder(encoder)->or;
 	u32 load = 0;
 
+	// Do not touch the hardware when the card is powered off
+	if (encoder->dev->switch_power_state != DRM_SWITCH_POWER_ON)
+		return connector_status_unknown;
+
 	ret = nv_exec(disp->core, NV50_DISP_DAC_LOAD + or, &load, sizeof(load));
 	if (ret || load != 7)
 		return connector_status_disconnected;