vp9: Update last_q for dropped frames

last_q is used in resize logic, should
always be last Q selected for previous
frame, encoded or dropped.

Change-Id: Ie9019ccf5a9e3acc8456a2e70cc2aa8d1c90236e
diff --git a/vp9/encoder/vp9_ratectrl.c b/vp9/encoder/vp9_ratectrl.c
index 7301e80..c8b3e0b 100644
--- a/vp9/encoder/vp9_ratectrl.c
+++ b/vp9/encoder/vp9_ratectrl.c
@@ -1986,6 +1986,7 @@
   cpi->rc.rc_2_frame = 0;
   cpi->rc.rc_1_frame = 0;
   cpi->rc.last_avg_frame_bandwidth = cpi->rc.avg_frame_bandwidth;
+  cpi->rc.last_q[INTER_FRAME] = cpi->common.base_qindex;
   // For SVC on dropped frame when framedrop_mode != LAYER_DROP:
   // in this mode the whole superframe may be dropped if only a single layer
   // has buffer underflow (below threshold). Since this can then lead to