staging: panel: Use defined value or checking module params state

Avoid magic number and use a comparison with a defined value instead
that checks whether module param has been set by the user to some
value at loading time.

Signed-off-by: Mariusz Gorski <marius.gorski@gmail.com>
Acked-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>