gralloc: fix warnings

Fix LP64 pointer casting warnings, unused parameters, and
turn off missing initializer warnings.

Change-Id: Idb70f4534282fed64ae81cb1e154d3f5b93091b0
diff --git a/modules/gralloc/gralloc.cpp b/modules/gralloc/gralloc.cpp
index f832f35..bdc789d 100644
--- a/modules/gralloc/gralloc.cpp
+++ b/modules/gralloc/gralloc.cpp
@@ -166,7 +166,7 @@
 }
 
 static int gralloc_alloc_buffer(alloc_device_t* dev,
-        size_t size, int usage, buffer_handle_t* pHandle)
+        size_t size, int /*usage*/, buffer_handle_t* pHandle)
 {
     int err = 0;
     int fd = -1;