vp9: fix definition for VP9E_SET_POSTENCODE_DROP

(cherry picked from commit 24614dd9cb1ec6d5c946909ff17adf53d6aa2e54)

Change-Id: Ie763cf801107639ad11ad625408670d8d70b7628
diff --git a/vpx/vp8cx.h b/vpx/vp8cx.h
index 8d38c98..b2d57dc 100644
--- a/vpx/vp8cx.h
+++ b/vpx/vp8cx.h
@@ -1015,6 +1015,9 @@
                   vpx_svc_spatial_layer_sync_t *)
 #define VPX_CTRL_VP9E_SET_SVC_SPATIAL_LAYER_SYNC
 
+VPX_CTRL_USE_TYPE(VP9E_SET_POSTENCODE_DROP, unsigned int)
+#define VPX_CTRL_VP9E_SET_POSTENCODE_DROP
+
 /*!\endcond */
 /*! @} - end defgroup vp8_encoder */
 #ifdef __cplusplus