Fix bad shader code

Shader code missing "=" in a couple of cases.

Change-Id: Iff8a99a0ccb2903c30e2bdb2f698ef9b2e03d5d1
diff --git a/libs/hwui/ProgramCache.cpp b/libs/hwui/ProgramCache.cpp
index 6e7f35d..2d13f60 100644
--- a/libs/hwui/ProgramCache.cpp
+++ b/libs/hwui/ProgramCache.cpp
@@ -231,10 +231,10 @@
 };
 const char* gFS_Fast_SingleModulateGradient[2] = {
         "\nvoid main(void) {\n"
-        "    gl_FragColor " FS_MAIN_DITHER " + color.a * texture2D(gradientSampler, linear);\n"
+        "    gl_FragColor = " FS_MAIN_DITHER " + color.a * texture2D(gradientSampler, linear);\n"
         "}\n\n",
         "\nvoid main(void) {\n"
-        "    gl_FragColor " FS_MAIN_DITHER " + color.a * mix(startColor, endColor, clamp(linear, 0.0, 1.0));\n"
+        "    gl_FragColor = " FS_MAIN_DITHER " + color.a * mix(startColor, endColor, clamp(linear, 0.0, 1.0));\n"
         "}\n\n"
 };