powerpc: Fix comment around arch specific definition of RECLAIM_DISTANCE

Commit 32e45ff4 changed the default value of
RECLAIM_DISTANCE to 30. However the comment around arch
specifc definition of RECLAIM_DISTANCE is not updated to
reflect the same. Correct the value mentioned in the comment.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: KOSAKI Motohiro <Kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>