interval_tree: Sync interval_tree_generic.h with tools
The following commit made an improvement to interval_tree_generic.h, but
didn't sync it to the tools copy:
19811285784f ("lib/interval_tree: skip the check before go to the right subtree")
Sync it, and add it to objtool's sync-check.sh so they are more likely
to stay in sync going forward.
Acked-by: Petr Mladek <pmladek@suse.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>