Fix IOCs

A left shift of negative value causes IOC runtime warnings, this
commit converts two such left shifts to multiply to avoid IOCs.

Change-Id: I8811428768d7135e6e16af4b3094d0341589a995

vp8/encoder/mcomp.c

@@ -393,8 +393,8 @@ int vp8_find_best_sub_pixel_step(MACROBLOCK *x, BLOCK *b, BLOCKD *d,
 #endif
 
     /* central mv */
-    bestmv->as_mv.row <<= 3;
-    bestmv->as_mv.col <<= 3;
+    bestmv->as_mv.row *= 8;
+    bestmv->as_mv.col *= 8;
     startmv = *bestmv;
 
     /* calculate central point error */