stagefright: Fix encoder startup failure on 7x27

Framerate value on output port can't be zero, that value causes the
encoder init to abort entirely.
Higher values must be used, and on 7x27 VidEnc it apparently must match
the input bitrate, since the value is used for rate control. Lower values
result in:

E/VENC_ENC( 2565): VENC_ERROR venci_do_rate_control_camcorder::5077 time delta is less than 1
E/VENC_ENC( 2565): VENC_ERROR venci_arm_encode::5586 time delta is less than 1

Change-Id: I7070514040e5bdedae7f360fa4df502bca158439