video: msm: wfd: Remove the need for scratch buffer by VSG

VSG has until now needed a scratch buffer to memcpy YUV frames into as
the video driver had a limitation of not being to accept the same
buffer consecutive times.  This restriction no longer applies. Hence,
remove all references to the scratch buffer.

Change-Id: Idc835296f5b4b8063529f5ac914956c69e809500
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>
CRs-Fixed: 341405