msm: camera: Use round rate to calculate bus vector

Bus vector should be calculated based on vfe clock rate.
Vfe clock rate requested from userspace might not be the same
as the rate from the clock plan. This change make sure the
calculation is using the rounded rate which is from the clock plan.

Change-Id: Ic63ed751112d75a71b24a432b9cbc7dc59cac0a3
Signed-off-by: Kevin Chan <ktchan@codeaurora.org>