vfs: Rename fsync_super() to sync_filesystem() (version 4)

Rename the function so that it better describe what it really does. Also
remove the unnecessary include of buffer_head.h.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index 1e96234..dafd484 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -354,7 +354,7 @@
 	/* make sure all pages pinned by operations on behalf of the netfs are
 	 * written to disc */
 	cachefiles_begin_secure(cache, &saved_cred);
-	ret = fsync_super(cache->mnt->mnt_sb);
+	ret = sync_filesystem(cache->mnt->mnt_sb);
 	cachefiles_end_secure(cache, saved_cred);
 
 	if (ret == -EIO)