msm: vidc: fix dpb buffer count validation

Shouldn't use count_min to validate dpb buffer count, as it
has already been modified when received seq change event.
Use dpb buffer_count_actual instead.

Change-Id: Iad4117e4d0045859312d726caae1c8801ba1b897
Signed-off-by: Qiwei Liu <qiweil@codeaurora.org>