media: dvb: mpq: Decreased YUV buffers to 12

Decreased the number of YUV buffers for video decoder from 15 to 12.
Video Decoding Failed as ION memory is not available for 15 Buffers
during dvb end to end verification.

Change-Id: I91f90d6be9548e624bf8a1d5c33c51ebe0f1fd3b
Signed-off-by: Ananda Kishore <kananda@codeaurora.org>