ACPI: add missing win8 OSI comment to blacklist

In my original patch[1] I wrote a comment describing the reason for
disabling Windows 2012 OSI mode for a group of machines, however, due to
unknown reasons (probably a conflict resolution mismatch), the comment
was dropped in 94fb982 (ACPI: blacklist win8 OSI for buggy laptops).

Since Matthew Garrett is making a big deal out of the lack of comments
in a separate patch[2], it might make sense to re-introduce the missing
comment so that other patch is not blocked and users don't suffer.

[1] http://article.gmane.org/gmane.linux.acpi.devel/63427
[2] http://thread.gmane.org/gmane.linux.kernel/1572459

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/blacklist.c

@@ -273,6 +273,11 @@ static struct dmi_system_id acpi_osi_dmi_table[] __initdata = {
 		     DMI_MATCH(DMI_PRODUCT_NAME, "Satellite P305D"),
 		},
 	},
+
+	/*
+	 * The following machines have broken backlight support when reporting
+	 * the Windows 2012 OSI, so disable it until their support is fixed.
+	 */
 	{
 	.callback = dmi_disable_osi_win8,
 	.ident = "ASUS Zenbook Prime UX31A",