orangefs: rename remaining bits of mmap readahead cache

This has been dormant code for many years. Parts of it were removed from
the OrangeFS kernel code when it went into mainline. These bits were missed.
Now the readahead cache has been resurrected in the OrangeFS userspace
portions. It was renamed there, since it doesn't really have anything to do
with mmap specifically, so it will be renamed here.

Signed-off-by: Martin Brandenburg <martin@omnibond.com>

fs/orangefs/file.c

@@ -591,7 +591,7 @@ static int orangefs_file_release(struct inode *inode, struct file *file)
 	orangefs_flush_inode(inode);
 
 	/*
-	 * remove all associated inode pages from the page cache and mmap
+	 * remove all associated inode pages from the page cache and
 	 * readahead cache (if any); this forces an expensive refresh of
 	 * data for the next caller of mmap (or 'get_block' accesses)
 	 */