mm-video: fix arithmetic on a pointer to void

Summary:
Use char* instead of void* for this
pointer arithmetic. Fixes the following:

error: arithmetic on a pointer to void
(vdec_msg->msgdata.output_frame.bufferaddr +

Test Plan: verified

Reviewers: randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D624
mm-video: fix string literals for c++11

Summary: ...

Test Plan: verified

Reviewers: randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D625