ARM: dts: msm: change PS_THRESHOLD for LAB regulator to 20 mA

Currently, pulse skip (PS) threshold for LAB regulator is
configured to 40 mA. However, it should be configured to 20 mA
as per the recommendation from systems team. Change it.

CRs-Fixed: 807716
Change-Id: I077b2958a8801c9c8de654a34914cee7ca467ea0
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>