mm/damon/core: disallow non-power of two min_region_sz on damon_start()

mm/damon/core: disallow non-power of two min_region_sz on damon_start()

Commit d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region") introduced
a bug that allows unaligned DAMON region address ranges.  Commit
c80f46ac228b ("mm/damon/core: disallow non-power of two min_region_sz")
fixed it, but only for damon_commit_ctx() use case.  Still, DAMON sysfs
interface can emit non-power of two min_region_sz via damon_start().  Fix
the path by adding the is_power_of_2() check on damon_start().

The issue was discovered by sashiko [1].

Link: https://lore.kernel.org/20260411213638.77768-1-sj@kernel.org
Link: https://lore.kernel.org/20260403155530.64647-1-sj@kernel.org
Fixes: d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>