Refactor compound_segment to try different segmentation masks

Change-Id: I7c992c9aae895aebcfb5c147cb179cf665c0ac10
diff --git a/av1/decoder/decodemv.c b/av1/decoder/decodemv.c
index e07625d..ce2e30e 100644
--- a/av1/decoder/decodemv.c
+++ b/av1/decoder/decodemv.c
@@ -1888,7 +1888,8 @@
     }
 #if CONFIG_COMPOUND_SEGMENT
     else if (mbmi->interinter_compound_data.type == COMPOUND_SEG) {
-      mbmi->interinter_compound_data.which = aom_read_bit(r, ACCT_STR);
+      mbmi->interinter_compound_data.mask_type =
+          aom_read_literal(r, MAX_SEG_MASK_BITS, ACCT_STR);
     }
 #endif  // CONFIG_COMPOUND_SEGMENT
   }