Fix accidental activateTexture(0)

Bug: 26584230

activateTexture(0) was accidentally refactored into
Texture::upload. Only OffscreenBuffer intended for the
texture unit to change

Change-Id: I5dbfc3eab8843733084ce1ce38a0a946abf0e05b
diff --git a/libs/hwui/renderstate/OffscreenBufferPool.cpp b/libs/hwui/renderstate/OffscreenBufferPool.cpp
index 98c94df..54f38e8 100644
--- a/libs/hwui/renderstate/OffscreenBufferPool.cpp
+++ b/libs/hwui/renderstate/OffscreenBufferPool.cpp
@@ -41,6 +41,7 @@
         , texture(caches) {
     uint32_t width = computeIdealDimension(viewportWidth);
     uint32_t height = computeIdealDimension(viewportHeight);
+    caches.textureState().activateTexture(0);
     texture.resize(width, height, GL_RGBA);
     texture.blend = true;
     texture.setWrap(GL_CLAMP_TO_EDGE);