staging: dgnc: delete is_pci_express board type variable.

It was only set, and never looked at, so drop the thing as no one cares
about it.  And when it was set, it was not even set correctly, the index
it was using to read from was incorrect, so this has never even been
correct...

Cc: Lidza Louina <lidza.louina@gmail.com>
Cc: Mark Hounschell <markh@compro.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>