mm/damon: document damon_call_control->dealloc_on_cancel repeat behavior

mm/damon: document damon_call_control->dealloc_on_cancel repeat behavior

damon_call_control->dealloc_on_cancel works only when ->repeat is true.
But the behavior is not clearly documented.  DAMON API callers can
understand the behavior only after reading kdamond_call() code.  Document
the behavior on the kernel-doc comment of damon_call_control.

Link: https://lkml.kernel.org/r/20260117175256.82826-6-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>