__find_vmap_area() finds a "vmap_area" based on passed address.  It scan
the specific "vmap_area_root" rb-tree.  Extend the function with one extra
argument, so any tree can be specified where the search has to be done.

There is no functional change as a result of this patch.

Link: https://lkml.kernel.org/r/20220607093449.3100-5-urezki@gmail.comSigned-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>