open.2: Change pathname used in discussion of rationale for openat()

/path/to/file is a little confusing as a pathname

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/open.2

@@ -1476,14 +1476,14 @@ of the directory prefix given to
 could be changed in parallel with the call to
 .BR open ().
 Suppose, for example, that we wish to create the file
-.I path/to/xxx.dep
+.I dir1/dir2/xxx.dep
 if the file
-.I path/to/xxx
+.I dir1/dir2/xxx
 exists.
 The problem is that between the existence check and the file creation step,
-.I path
+.I dir1
 or
-.I to
+.I dir2
 (which might be symbolic links)
 could be modified to point to a different location.
 Such races can be avoided by