vold: suppress unused argument warning messages

(cherry picked from commit 3e971277db0d87652af5622c989233e7159ab909)

Change-Id: Ic1ab533f756fbd44b1f2e5ae12e2f5736ace7740
diff --git a/Volume.cpp b/Volume.cpp
index 80552b6..ca56d1c 100644
--- a/Volume.cpp
+++ b/Volume.cpp
@@ -147,7 +147,7 @@
 void Volume::handleVolumeUnshared() {
 }
 
-int Volume::handleBlockEvent(NetlinkEvent *evt) {
+int Volume::handleBlockEvent(NetlinkEvent * /*evt*/) {
     errno = ENOSYS;
     return -1;
 }