msm: cpr: Limit down step to avoid sudden drops

It has been observed that CPR could recommend more than 4 steps
down followed by equal steps up in certain load situations. To avoid
breaching the system level Vmin which is around 4 steps below, it
is safe to climb down 2 steps at a time and avoid any breach of
minimum voltage requirement. This allows CPR to re-sample and avoid
sudden drop from where it cannot recover.

Change-Id: I6e89cdff004f4fd775dfe33c0cfef45eee772a92
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>