msm: vidc: correct buffer size calcuation logic for output plane

if input format and resolution are same buffer size then
plane buffer size re-calculation is getting skipped,
due to this client not able to set custom buffer size.
Recalculate buffer sizes of output plane, when client
set valid custom buffer size.

Change-Id: I830040c311c3ffacf33c2b3d9ccb753e42970df9
Signed-off-by: Srinu Gorle <sgorle@codeaurora.org>