Rockchip: fix frame hdr overwritten error

frmHdrBufLen & frmhdr might be overwritten sometimes, which
may cause "Bad address" error when set ext ctrls.

BUG=chromium:497324
TEST=screen share through Hangouts, no more "Bad address"

Change-Id: I95d355139ca78bcb9e28a7ad018f80a71c14de34
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/277732


Reviewed-by: Justin Chuang <jchuang@chromium.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>