msm: vidc: Return min buffer count in VIDIOC_REQBUFS.

- If stream triggers multiple port reconfigure events, number of
  buffers required for output plane incremented due to actual
  buffer count returned from video driver.
- Minbuffer count should be return when buffer requirement called.

Change-Id: I943f2cfdd595b8278058b5bdcbbcf24c9f320440
Signed-off-by: Srinu Gorle <sgorle@codeaurora.org>