ACPI / video: ignore BIOS initial backlight value for HP m4

On HP m4 lapops, BIOS reports minimum backlight on boot and
causes backlight to dim completely. This ignores the initial backlight
values and set to max brightness.

References: https://bugs.launchpad.net/bugs/1184501


Cc: All <stable@vger.kernel.org>
Signed-off-by: Alex Hung <alex.hung@canonical.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>