S4 only has 8 texture units on the GLContext we create

BUG=skia:4373

Review URL: https://codereview.chromium.org/1386643002
diff --git a/bench/GLBench.cpp b/bench/GLBench.cpp
index e51adba..f184d77 100644
--- a/bench/GLBench.cpp
+++ b/bench/GLBench.cpp
@@ -110,7 +110,7 @@
     //Setup framebuffer
     GrGLuint texture;
     GR_GL_CALL(gl, GenTextures(1, &texture));
-    GR_GL_CALL(gl, ActiveTexture(GR_GL_TEXTURE15));
+    GR_GL_CALL(gl, ActiveTexture(GR_GL_TEXTURE7));
     GR_GL_CALL(gl, BindTexture(GR_GL_TEXTURE_2D, texture));
     GR_GL_CALL(gl, TexParameteri(GR_GL_TEXTURE_2D, GR_GL_TEXTURE_MAG_FILTER, GR_GL_NEAREST));
     GR_GL_CALL(gl, TexParameteri(GR_GL_TEXTURE_2D, GR_GL_TEXTURE_MIN_FILTER, GR_GL_NEAREST));