staging: dgnc: remove redundant NULL check for brd

the "brd" value cannot be NULL in dgnc_finalize_board_init().
Because "brd" as a parameter of this function was already
checked for NULL.

the dgnc_finalize_board_init() as a static function was called
only from dgnc_found_board() function and brd->magic value
was assigned once in dgnc_found_board(). So it doesn't need to
check for DGNC_BOARD_MAGIC value.

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