doc: inode uses a mutex instead of a semaphore.

Replace the introduced i_sem by an i_mutex in the filesystem locking
documentation. This was introduced [1] after all occurrences were
already replaced in the same text [2]. However, the term "inode
semaphore" has not been replaced then, and it's replaced now.

[1] afddba49d18f346e5cc2938b6ed7c512db18ca68
[2] a7bc02f4f47fd0e7860c6589f0ad000d1476f7a3

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/filesystems/Locking

@@ -178,7 +178,7 @@ prototypes:
 locking rules:
 	All except set_page_dirty may block
 
-			BKL	PageLocked(page)	i_sem
+			BKL	PageLocked(page)	i_mutex
 writepage:		no	yes, unlocks (see below)
 readpage:		no	yes, unlocks
 sync_page:		no	maybe
@@ -429,7 +429,7 @@ check_flags:		no
 implementations.  If your fs is not using generic_file_llseek, you
 need to acquire and release the appropriate locks in your ->llseek().
 For many filesystems, it is probably safe to acquire the inode
-semaphore.  Note some filesystems (i.e. remote ones) provide no
+mutex.  Note some filesystems (i.e. remote ones) provide no
 protection for i_size so you will need to use the BKL.
 
 Note: ext2_release() was *the* source of contention on fs-intensive