nvidiafb: remove usage of bl_mutex from nvidiafb_blank()

struct fb_info bl_mutex is used to protect bl_curve[] only, not needed in
nvidiafb_blank() and will cause a recursive mutex locking in
nvidia_bl_get_level_brightness()

Signed-off-by: Aristeu S. Rozanski F. <aris@valeta.org>

Index: ppc-2.6/drivers/video/nvidia/nvidia.c
===================================================================
--- ppc-2.6.orig/drivers/video/nvidia/nvidia.c	2006-07-03 20:08:07.000000000 -0300
+++ ppc-2.6/drivers/video/nvidia/nvidia.c	2006-07-03 20:08:16.000000000 -0300
@@ -934,14 +934,12 @@
 	NVWriteCrtc(par, 0x1a, vesa);
 
 #ifdef CONFIG_FB_NVIDIA_BACKLIGHT
-	mutex_lock(&info->bl_mutex);
 	if (info->bl_dev) {
 		down(&info->bl_dev->sem);
 		info->bl_dev->props->power = blank;
 		info->bl_dev->props->update_status(info->bl_dev);
 		up(&info->bl_dev->sem);
 	}
-	mutex_unlock(&info->bl_mutex);
 #endif
 
 	NVTRACE_LEAVE();