staging: dgap: unwind on error in dgap_found_board()

Adds a label for "kfree(brd)". And also remove
a state value as BOARD_FAILED in brd when dgap_do_remap() is failed.
Because "brd" will free after failure.

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>