Change to use 8bit for qmatrix entries

This is to reduce the size of static tables.

BUG=aomedia:1030

Change-Id: Id9a00352560af38eb381f403510ec3f3d7f1c29a
diff --git a/aom_dsp/aom_dsp_common.h b/aom_dsp/aom_dsp_common.h
index 2261e53..9b20566 100644
--- a/aom_dsp/aom_dsp_common.h
+++ b/aom_dsp/aom_dsp_common.h
@@ -52,7 +52,7 @@
 #define UNLIKELY(v) (v)
 #endif
 
-typedef uint16_t qm_val_t;
+typedef uint8_t qm_val_t;
 #define AOM_QM_BITS 5
 
 // Note: