mm/damon/paddr: improve readability of damon_pa_stat

mm/damon/paddr: improve readability of damon_pa_stat

damon_pa_stat contains an unnecessary goto statement, and the if/else can
be re-written to be more readable.

This patch is written on top of SJ's patch series [1], which in turn is
written on top of another one of his series [2].

[1] https://lore.kernel.org/all/20241219040327.61902-1-sj@kernel.org/
[2] https://lore.kernel.org/all/20241213215306.54778-1-sj@kernel.org/

Link: https://lkml.kernel.org/r/20250113210201.446051-1-joshua.hahnjy@gmail.com
Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>