lib/interval_tree: skip the check before go to the right subtree

The interval_tree_subtree_search() holds the loop invariant:

    start <= node->ITSUBTREE

Let's say we have a following tree:

         node
         /  \
      left  right

So we know node->ITSUBTREE is contributed by one of the following:

  * left->ITSUBTREE
  * ITLAST(node)
  * right->ITSUBTREE

When we come to the right node, we are sure the first two don't
contribute to node->ITSUBTREE and it must be the right node does the
job.

So skip the check before go to the right subtree.

Link: https://lkml.kernel.org/r/20250310074938.26756-7-richard.weiyang@gmail.com


Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michel Lespinasse <michel@lespinasse.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>