gralloc: Clean kernel allocated pmem buffers after memset

Change-Id: I1a13c38c38a9f321e3f163545d0331529d2f7e6f

libgralloc/pmemalloc.cpp

@@ -319,7 +319,7 @@ int PmemKernelAlloc::alloc_buffer(alloc_data& data)
         return err;
     }
     memset(base, 0, size);
-    //XXX: Flush here if cached
+    clean_buffer((void*)((intptr_t) base + offset), size, offset, fd);
     data.base = base;
     data.offset = 0;
     data.fd = fd;