staging: dgnc: remove redundant initialization for channel array

The channel array in board_t was initialized in dgnc_found_board()
with NULL. But the channel is going to initialize in dgnc_tty_init().
So the channel array doesn't need to set NULL for initailization.

Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>