pmic-voter: bump up from 8 clients to 16

The current code only supports 8 clients max. There are
situations where we will need more than that.

Bump it up to 16.

Change-Id: I7a32f67b3a4579ec79eb4f0e2a971a1a3a29a7c1
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>