mm/damon: needn't hold kdamond_lock to print pid of kdamond

Just get the pid by 'current->pid'.  Meanwhile, to be symmetrical make
the 'starts' and 'finishes' logs both use debug level.

Link: https://lkml.kernel.org/r/20210927232432.17750-1-changbin.du@gmail.com


Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>