Correct SPLITMV clamping

Prior to this fix, the clamping state of the last subblock partition
dominated, whereas the correct behavior is to clamp if any partition
needs clamping. This bug was introduced by v0.9.6-232-g6b25501

See also:
  [1]: http://code.google.com/p/webm/issues/detail?id=371
  [2]: https://bugzilla.mozilla.org/show_bug.cgi?id=696390

Change-Id: I444db492b4c4f05f039c7da6f4216da8207dc138

vp8/decoder/decodemv.c

@@ -273,6 +273,7 @@ static void decode_split_mv(vp8_reader *const bc, MODE_INFO *mi,
         }
     }
 
+    mbmi->need_to_clamp_mvs = 0;
     do  /* for each subset j */
     {
         int_mv leftmv, abovemv;
@@ -289,7 +290,7 @@ static void decode_split_mv(vp8_reader *const bc, MODE_INFO *mi,
 
         blockmv = sub_mv_ref(bc, prob, abovemv, leftmv, best_mv, mvc);
 
-        mbmi->need_to_clamp_mvs = vp8_check_mv_bounds(&blockmv,
+        mbmi->need_to_clamp_mvs |= vp8_check_mv_bounds(&blockmv,
                                                   mb_to_left_edge,
                                                   mb_to_right_edge,
                                                   mb_to_top_edge,