android: add helper to convert buffer_handle_t to gralloc_handle_t ptr

Clients frequently need to convert a buffer_handle_t (aka
native_handle_t *) to a gralloc_handle_t ptr. This is a simple cast, but
add an inline function to do the conversion.

Reviewed-by: Robert Foss <robert.foss@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>

android/gralloc_handle.h

@@ -76,6 +76,11 @@ struct gralloc_handle_t {
 	((sizeof(struct gralloc_handle_t) - sizeof(native_handle_t))/sizeof(int))	\
 	 - GRALLOC_HANDLE_NUM_FDS)
 
+static inline struct gralloc_handle_t *gralloc_handle(buffer_handle_t handle)
+{
+	return (struct gralloc_handle_t *)handle;
+}
+
 /**
  * Create a buffer handle.
  */