radix tree: remove unused variable

Recent versions of clang warn about an unused variable, though older
versions saw the 'slot++' as a use and did not warn:

radix-tree.c:1136:50: error: parameter 'slot' set but not used [-Werror,-Wunused-but-set-parameter]

It's clearly not needed any more, so just remove it.

Link: https://lkml.kernel.org/r/20230811131023.2226509-1-arnd@kernel.org
Fixes: 3a08cd52c3 ("radix tree: Remove multiorder support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Rong Tao <rongtao@cestc.cn>
Cc: Tom Rix <trix@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/radix-tree.c

@@ -1136,7 +1136,6 @@ static void set_iter_tags(struct radix_tree_iter *iter,
 void __rcu **radix_tree_iter_resume(void __rcu **slot,
 					struct radix_tree_iter *iter)
 {
-	slot++;
 	iter->index = __radix_tree_iter_add(iter, 1);
 	iter->next_index = iter->index;
 	iter->tags = 0;