msm: vidc: Update plane count in get-format

Currently, driver updates plane count only when client
requests buffer requirements. If it queries buffer
format before requesting buffer requirement, driver
returns incorrect plane count. With this change,
driver updates plane count in get-format as well.

CRs-Fixed: 1021026
Change-Id: Id829f07123963584f6c7fe0174e34006d2697aa9
Signed-off-by: Saurabh Kothawade <skothawa@codeaurora.org>