Documentation: Fix trivial typo in filesystems/sharedsubtree.txt

Documentation: Fix trivial typo in filesystems/sharedsubtree.txt

This typo is easy to ignore unless you have spent a great deal of time
thinking about how to eliminate duplicate dentries in unions.

Signed-off-by: Valerie Aurora <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

Documentation/filesystems/sharedsubtree.txt

···
 	# mount /dev/sd0  /tmp/a
 
 	#ls /tmp/a
-	t1 t2 t2
+	t1 t2 t3
 
 	#ls /mnt/a
-	t1 t2 t2
+	t1 t2 t3
 
 	Note that the mount has propagated to the mount at /mnt as well.