[PATCH] export unmap_underlying__metadata()

From Anton Altaparmakov

The below bk patch against your current bk repository adds an export
for fs/buffer.c::unmap_underlying_metadata() to modules.

It is required to make ntfs compile as a module in the current kernel.

Note that NTFS doesn't currently dirty bufferheads of the underlying
blockdevice and as such could probably live without calling
unmap_underlying_metadata() but as soon as we enable writing to
compressed files it will do so and considering some of the
infrastructure code is already present I would rather not rip it out
now.

fs/buffer.c

@@ -1622,6 +1622,7 @@ void unmap_underlying_metadata(struct block_device *bdev, sector_t block)
 		__brelse(old_bh);
 	}
 }
+EXPORT_SYMBOL(unmap_underlying_metadata);
 
 /*
  * NOTE! All mapped/uptodate combinations are valid: