mm/damon/sysfs: use damon_commit_ctx()

DAMON_SYSFS manually manipulates DAMON context structs for online
parameters update.  Since the struct contains not only input parameters
but also internal status and operation results, it is not that simple. 
Indeed, we found and fixed a few bugs in the code.  Now DAMON core layer
provides a function for the usage, namely damon_commit_ctx().  Replace the
manual manipulation logic with the function.  The core layer function
could have its own bugs, but this change removes a source of bugs.

Link: https://lkml.kernel.org/r/20240618181809.82078-4-sj@kernel.org


Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>