Added default return value to transform selector

The non-void function didn't return a value in the default case.

Change-Id: Ie4c965315bedc189d2080dd65cf29d3347661946

vp8/common/blockd.h

@@ -505,6 +505,7 @@ static TX_TYPE get_tx_type(MACROBLOCKD *xd, BLOCKD *b) {
     return tx_type;
   }
 #endif
+  return tx_type;
 }
 #endif