mm/damon/vaddr: put pid in cleanup_target()

mm/damon/vaddr: put pid in cleanup_target()

Implement cleanup_target() callback for [f]vaddr, which calls put_pid()
for each target that will be destroyed.  Also remove redundant put_pid()
calls in core, sysfs and sample modules, which were required to be done
redundantly due to the lack of such self cleanup in vaddr.

Link: https://lkml.kernel.org/r/20250712195016.151108-11-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>