vold: suppress unused argument warning messages

Change-Id: Ic1ab533f756fbd44b1f2e5ae12e2f5736ace7740
diff --git a/Loop.cpp b/Loop.cpp
index 78df132..3f0ee1e 100644
--- a/Loop.cpp
+++ b/Loop.cpp
@@ -227,7 +227,7 @@
     return 0;
 }
 
-int Loop::destroyByFile(const char *loopFile) {
+int Loop::destroyByFile(const char * /*loopFile*/) {
     errno = ENOSYS;
     return -1;
 }