autofs: fix typos in Documentation/filesystems/autofs4.txt

plus minor whitespace fixes.

Link: http://lkml.kernel.org/r/20160812024734.12352.17122.stgit@pluto.themaw.netSigned-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/filesystems/autofs4.txt

@@ -203,7 +203,7 @@ initiated or is being considered, otherwise it returns 0.
 Mountpoint expiry
 -----------------
 
-The VFS has a mechansim for automatically expiring unused mounts,
+The VFS has a mechanism for automatically expiring unused mounts,
 much as it can expire any unused dentry information from the dcache.
 This is guided by the MNT_SHRINKABLE flag.  This only applies to
 mounts that were created by `d_automount()` returning a filesystem to be
@@ -298,7 +298,7 @@ remove directories and symlinks using normal filesystem operations.
 autofs knows whether a process requesting some operation is the daemon
 or not based on its process-group id number (see getpgid(1)).
 
-When an autofs filesystem it mounted the pgid of the mounting
+When an autofs filesystem is mounted the pgid of the mounting
 processes is recorded unless the "pgrp=" option is given, in which
 case that number is recorded instead.  Any request arriving from a
 process in that process group is considered to come from the daemon.