mm/kmemleak.c: make cond_resched() rate-limiting more efficient

Commit bde5f6bc ("kmemleak: add scheduling point to
kmemleak_scan()") tries to rate-limit the frequency of cond_resched()
calls, but does it in a way which might incur an expensive division
operation in the inner loop.  Simplify this.

Fixes: bde5f6bc ("kmemleak: add scheduling point to kmemleak_scan()")
Suggested-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Yisheng Xie <xieyisheng1@huawei.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/kmemleak.c

@@ -1523,7 +1523,7 @@ static void kmemleak_scan(void)
 			if (page_count(page) == 0)
 				continue;
 			scan_block(page, page + 1, NULL);
-			if (!(pfn % (MAX_SCAN_SIZE / sizeof(*page))))
+			if (!(pfn & 63))
 				cond_resched();
 		}
 	}