Use const auto&/auto&& in adb.

Change-Id: I74a7e511302e15e207906f572d181634e0ed5604
diff --git a/adb/adb.cpp b/adb/adb.cpp
index 3dcf282..1eb3a3c 100644
--- a/adb/adb.cpp
+++ b/adb/adb.cpp
@@ -245,7 +245,7 @@
 
     if (pieces.size() > 2) {
         const std::string& props = pieces[2];
-        for (auto& prop : android::base::Split(props, ";")) {
+        for (const auto& prop : android::base::Split(props, ";")) {
             // The list of properties was traditionally ;-terminated rather than ;-separated.
             if (prop.empty()) continue;