rename yuv matrix constants to be more clear about what they are

source/planar_functions.cc

Index: source/planar_functions.cc
diff --git a/source/planar_functions.cc b/source/planar_functions.cc
index 900a35e7b9f80756d6b87964e3da745c2f0cd903..f3d51714790dd766cf14872e27f66df8846f59dc 100644
--- a/source/planar_functions.cc
+++ b/source/planar_functions.cc
@@ -843,7 +843,7 @@ int I422ToRGBA(const uint8* src_y, int src_stride_y,
                           src_u, src_stride_u,
                           src_v, src_stride_v,
                           dst_rgba, dst_stride_rgba,
-                          &kYuvIConstants,
+                          &kYuvI601Constants,
                           width, height);
 }
 
@@ -910,7 +910,7 @@ int NV12ToRGB565(const uint8* src_y, int src_stride_y,
 #endif
 
   for (y = 0; y < height; ++y) {
-    NV12ToRGB565Row(src_y, src_uv, dst_rgb565, &kYuvIConstants, width);
+    NV12ToRGB565Row(src_y, src_uv, dst_rgb565, &kYuvI601Constants, width);
     dst_rgb565 += dst_stride_rgb565;
     src_y += src_stride_y;
     if (y & 1) {