msm: vidc: Re-calculate buffer requirement

During certain video usecase, the DPB-OPB mode is
changed from split mode to combined mode. Doing so,
video firmware does not update the buffer requirement
as per the new mode. As a result, firmware has buffer
size of output buffer calculated earlier with UBWC format
whereas video driver has buffer size of output buffer
calculated with NV12 format. Due to this, it asserts
while doing buffer size comparasion inside firmware.
This code now requests firmware to update buffer
requirement when changing mode from split to combined.

Change-Id: Ief9b4a4e8dd8d8b75fcab979633a674e03483390
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>