ACPI / video: correct DMI tag for Dell Inspiron 7520

The DMI tag used to identify Dell Inspiron 7520 should be product name
instead of product version.

Fixes: 0e9f81d3 (ACPI / video: Add systems that should favour native backlight interface)
Reported-and-tested-by: Téo Mazars <teomazars@gmail.com>
References: https://bugzilla.redhat.com/show_bug.cgi?id=909552


Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>