gralloc: Default to an error value for mapFrameBuffer

We do further operations in fb_device_open based on the result of
mapFrameBuffer. However, if mapFrameBuffer is never done, we
could end up with a random crash when using the info values in
fb_device_open. Defaulting to an error value avoids this.

Change-Id: I1e51f814611a3f2eb73f36d75e14d8725ca98474
diff --git a/libgralloc/framebuffer.cpp b/libgralloc/framebuffer.cpp
index 1851196..3109303 100644
--- a/libgralloc/framebuffer.cpp
+++ b/libgralloc/framebuffer.cpp
@@ -336,7 +336,7 @@
 
 static int mapFrameBuffer(struct private_module_t* module)
 {
-    int err = 0;
+    int err = -1;
     char property[PROPERTY_VALUE_MAX];
     if((property_get("debug.gralloc.map_fb_memory", property, NULL) > 0) &&
        (!strncmp(property, "1", PROPERTY_VALUE_MAX ) ||