Moved call to vp9_clear_system_state() to a proper location

The commit moved a call to vp9_clear_system_state() to a correct
location, i.e. prior function calls using floating point numbers.
This was to fix a mismatch mmx code and sse2 version, where a
floating point number used in adjust_frame_rate(cpi) gets NAN due
to mmx registers being in wrong state.

Change-Id: I40e0a6de98812000ccee6a729badb630604fd7e6