msm: camera: isp: Set UB to equal if master slave mode

UB policy is proportional by default which helps to avoid
overflow. But that leaves no UB left for 2nd session. Hence
equal policy is needed for master slave mode. Set it to equal
only for master slave mode so in normal usecase there is
better protection from bus overflow.

Change-Id: I4104cdd506c6e7197ba0e49e6b58d7d85231bcb1
Signed-off-by: Harsh Shah <harshs@codeaurora.org>