selftests/ublk: fix garbage output in foreground mode

Initialize _evtfd to -1 in struct dev_ctx to prevent garbage output
when running kublk in foreground mode. Without this, _evtfd is
zero-initialized to 0 (stdin), and ublk_send_dev_event() writes
binary data to stdin which appears as garbage on the terminal.

Also fix debug message format string.

Fixes: 6aecda0 ("selftests: ublk: add kernel selftests for ublk")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Ming Lei

tools/testing/selftests/ublk/kublk.c

@@ -1274,7 +1274,7 @@ static int __cmd_dev_add(const struct dev_ctx *ctx)
 	}
 
 	ret = ublk_start_daemon(ctx, dev);
-	ublk_dbg(UBLK_DBG_DEV, "%s: daemon exit %d\b", ret);
+	ublk_dbg(UBLK_DBG_DEV, "%s: daemon exit %d\n", __func__, ret);
 	if (ret < 0)
 		ublk_ctrl_del_dev(dev);
 
@@ -1620,6 +1620,7 @@ int main(int argc, char *argv[])
 	int option_idx, opt;
 	const char *cmd = argv[1];
 	struct dev_ctx ctx = {
+		._evtfd         =       -1,
 		.queue_depth	=	128,
 		.nr_hw_queues	=	2,
 		.dev_id		=	-1,