msm: camera: cpas: Allow 0 votes in update ahb, axi apis

Allow clients to call update ahb, axi apis with 0 bw values
and use default minimum vote values inside cpas apis in such
cases. Accepting 0 bw values in update functions and voting
the same to bus driver would eventually cause failure in
further clk enable/disable apis.

Change-Id: I9a4c5e106f6e6991604782ce48c7bc690093be23
Signed-off-by: Pavan Kumar Chilamkurthi <pchilamk@codeaurora.org>