cmd: fix compile error in DEBUG

cmd is a std::string_view, not a char*

Test: compile with #define DEBUG 1
Change-Id: If5950f526bd30c339d8d183a9dd1b48860095d1c
diff --git a/cmds/cmd/cmd.cpp b/cmds/cmd/cmd.cpp
index 7b4aeb2..8dad475 100644
--- a/cmds/cmd/cmd.cpp
+++ b/cmds/cmd/cmd.cpp
@@ -223,7 +223,8 @@
     sp<MyResultReceiver> result = new MyResultReceiver();
 
 #if DEBUG
-    ALOGD("cmd: Invoking %s in=%d, out=%d, err=%d", cmd, in, out, err);
+    ALOGD("cmd: Invoking %.*s in=%d, out=%d, err=%d",
+          static_cast<int>(cmd.size()), cmd.data(), in, out, err);
 #endif
 
     // TODO: block until a result is returned to MyResultReceiver.