staging: dgap: make dgap_found_board() return a brd pointer

Make dgap_found_board() return a brd pointer and that brd pointer
assign to dgap_board[] in the end of the dgap_init_one().

Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>