docs: vfs: fix typo in struct xattr_handlers

The structure is called struct xattr_handler, singular, not plural.
Fixing the typo also makes it greppable with the whole word matching
flag.
Signed-off-by: Ariel Miculas <amiculas@cisco.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20231027152101.226296-1-amiculas@cisco.com>

Documentation/filesystems/vfs.rst

@@ -437,7 +437,7 @@ field.  This is a pointer to a "struct inode_operations" which describes
 the methods that can be performed on individual inodes.
 
 
-struct xattr_handlers
+struct xattr_handler
 ---------------------
 
 On filesystems that support extended attributes (xattrs), the s_xattr