Fix convert8To4, convert8To5

See b/5680952 "Compilation warnings in etc1.cpp" for discussion.

Fixes b/5680952

Change-Id: I0af6ba5ed5e60f3ed7a6a28eba3b09504fee1a3f
diff --git a/opengl/libs/ETC1/etc1.cpp b/opengl/libs/ETC1/etc1.cpp
index 5ed2c3c..97d1085 100644
--- a/opengl/libs/ETC1/etc1.cpp
+++ b/opengl/libs/ETC1/etc1.cpp
@@ -149,13 +149,13 @@
 static
 inline int convert8To4(int b) {
     int c = b & 0xff;
-    return divideBy255(b * 15);
+    return divideBy255(c * 15);
 }
 
 static
 inline int convert8To5(int b) {
     int c = b & 0xff;
-    return divideBy255(b * 31);
+    return divideBy255(c * 31);
 }
 
 static