[patch] mtd: use correct error codes in debugfs_create()

[Dan Carpenter]

The debugfs API is a bit confusing initialy but it's straight
foward to use.  You call:

	dfs_rootdir = debugfs_create_dir(...);

If it returns NULL then you return an error code.  If debugfs is
not enabled then it returns ERR_PTR(-ENODEV) but you don't normally
need to test for it.  After all later when you call:

	debugfs_create_file("wear_report", S_IRUSR,
			    dfs_rootdir, dev, &dfs_fops);

That function is just a no-op because debugfs is disabled.

The problem here is that we test for IS_ERR_OR_NULL() instead of
just if (!dfs_rootdir) which is wrong.  Also if we do hit an error
we return success because the true false bit are reversed.

regards,
dan carpenter
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