msm: vidc: Specify the number of planes in buffer to client

When a V4L2 client sets or gets the format, driver is supposed to report
back the dimensions, the size of the buffer, and the number of planes
contained with in the buffer.  The former two were being reported back
to the client, while the latter wasn't.

Change-Id: Ie225e108ce90cc40823ee9c0f13aeb7d054f5bdb
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>