fbdev: fix snprintf() limit in show_bl_curve()

The limit should be "PAGE_SIZE - len" instead of PAGE_SIZE. Also let's
use scnprintf() because snprintf() returns the number of bytes which
would have been printed if there were space and scnprintf() returns the
number of bytes actually printed.

I don't think we are ever going to actually hit this limit in real life.

Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Tomi Valkeinen <[e-mail]>

drivers/video/fbdev/core/fbsysfs.c

···
 
 	mutex_lock(&fb_info->bl_curve_mutex);
 	for (i = 0; i < FB_BACKLIGHT_LEVELS; i += 8)
-		len += snprintf(&buf[len], PAGE_SIZE, "%8ph\n",
+		len += scnprintf(&buf[len], PAGE_SIZE - len, "%8ph\n",
 				fb_info->bl_curve + i);
 	mutex_unlock(&fb_info->bl_curve_mutex);