adb: Avoid extra std::string copies

When a function argument takes a std::string, it's inefficient to
pass std::string::c_str(), since that creates an additional copy.
So we change these calling sites.

Test: TreeHugger
Change-Id: I1c0fde7275eb3ebd3baf05ec62581b0243655608
diff --git a/adb/services.cpp b/adb/services.cpp
index 80f9f79..cf346ba 100644
--- a/adb/services.cpp
+++ b/adb/services.cpp
@@ -188,7 +188,7 @@
     if (!strncmp(host.c_str(), "emu:", 4)) {
         connect_emulator(host.c_str() + 4, &response);
     } else {
-        connect_device(host.c_str(), &response);
+        connect_device(host, &response);
     }
 
     // Send response for emulator and device