UPSTREAM: mm/damon/core: mark damon_moving_sum() as a static function

The function is used by only mm/damon/core.c.  Mark it as a static
function.

Link: https://lkml.kernel.org/r/20230915025251.72816-9-sj@kernel.org



Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 863803a7)

Bug:407463672

Change-Id: I5a38ca01a9a50e5838d7e34031cf492840729a13
Signed-off-by: daiyang5 <daiyang5@xiaomi.com>