ntb: Remove error checking for debugfs_create_dir()

It is expected that most callers should _ignore_ the errors
return by debugfs_create_dir() in tool_setup_dbgfs()

Signed-off-by: Wang Ming <machel@vivo.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

Author: Wang Ming

drivers/ntb/test/ntb_tool.c

@@ -1495,8 +1495,6 @@ static void tool_setup_dbgfs(struct tool_ctx *tc)
 
 	tc->dbgfs_dir = debugfs_create_dir(dev_name(&tc->ntb->dev),
 					   tool_dbgfs_topdir);
-	if (!tc->dbgfs_dir)
-		return;
 
 	debugfs_create_file("port", 0600, tc->dbgfs_dir,
 			    tc, &tool_port_fops);