i8k: Use driver_data field of dmi_system_id to override fan multiplier

At least on Studio 1555 and XPS M140, the fan speed is reported directly,
not with the default speed multiplier of 30. Information on the web
suggests that this may be true for other models as well, though it is
unknown at this time which systems may be affected.

Use the driver_data field of dmi_system_id to override the default fan
multiplier value for the two systems known to use a multiplier of 1.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>