devtmpfs: get rid of bogus mkdir in create_path()

We do _NOT_ want to mkdir the path itself - we are preparing to
mknod it, after all.  Normally it'll fail with -ENOENT and
just do nothing, but if somebody has created the parent in
the meanwhile, we'll get buggered...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>