PNP: fix broken pnp lowercasing for acpi module aliases

Based on a patch from Brian, who identified the issue.

Signed-off-by: Bryan Kadzban <bryan@kadzban.is-a-geek.net>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>