venc: cleanup some cache operations
venc: cleanup some cache operations

After writing, we need to clean(), and there's no need to invalidate()
after mmaping; the cache is already flushed.

Signed-off-by: Felipe Contreras <de77a8b9cd239b204c19c52ed62e48ab47243362@gmail.com>

community-ssu/gst-dsp,felipec/gst-dsp,community-ssu/gst-dsp,community-ssu/gst-dsp,felipec/gst-dsp