Update IMemory.hal comments.

There was some confusion about the guarantees that getPointer made which
are now resolved.

Test: pass
Change-Id: I9c1783031c24018a262d4cf523e196f38d09fb89
diff --git a/transport/memory/1.0/IMemory.hal b/transport/memory/1.0/IMemory.hal
index 1b38336..404675a 100644
--- a/transport/memory/1.0/IMemory.hal
+++ b/transport/memory/1.0/IMemory.hal
@@ -29,6 +29,9 @@
     commit();
 
     /**
+     * Must return the same value everytime it is called. Must be callable
+     * at any point in or outside of the update/commit process.
+     *
      * @return ptr Actual pointer to underlying memory.
      */
     getPointer() generates (pointer ptr);