mm/damon/sysfs: rename damon_sysfs_set_targets() to ...add_targets()

mm/damon/sysfs: rename damon_sysfs_set_targets() to ...add_targets()

The function was for updating DAMON structs that may or may not be
partially populated.  Hence it was not for only adding items, but also
removing unnecessary items and updating items in-place.  A previous commit
has changed the function to assume the structs are not partially
populated, and do only adding items.  Make the function name better
explain the behavior.

Link: https://lkml.kernel.org/r/20240618181809.82078-7-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>