staging: dgnc: renames board_t to dgnc_board

This patch renames the struct board_t to dgnc_board. board_t
wasn't a good name for it since the _t suffix is for typedefs.

Signed-off-by: Lidza Louina <lidza.louina@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>