staging: dgnc: kfree for board structure in dgnc_found_board()

The board structure should be freed when any function was failed
in dgnc_found_board(). And the board strucure will be stored
into dgnc_board array when the dgnc_found_board() function has no error.

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