adb: Avoid a couple std::string constructions

With some internal API changing from "const char*" to
"const std::string&", we can change a couple calling sites to
directly pass a std::string reference, instead of getting the
c_str() version of the string.  This avoids us creating a
temporary std::string for the call.

Test: TreeHugger
Change-Id: I2fe0760ce8bf7d352010a341005356c0a801d351
diff --git a/adb/client/file_sync_client.cpp b/adb/client/file_sync_client.cpp
index cc38926..04ad536 100644
--- a/adb/client/file_sync_client.cpp
+++ b/adb/client/file_sync_client.cpp
@@ -1097,14 +1097,14 @@
         }
     };
 
-    if (!sync_ls(sc, rpath.c_str(), callback)) {
+    if (!sync_ls(sc, rpath, callback)) {
         return false;
     }
 
     // Check each symlink we found to see whether it's a file or directory.
     for (copyinfo& link_ci : linklist) {
         struct stat st;
-        if (!sync_stat_fallback(sc, link_ci.rpath.c_str(), &st)) {
+        if (!sync_stat_fallback(sc, link_ci.rpath, &st)) {
             sc.Warning("stat failed for path %s: %s", link_ci.rpath.c_str(), strerror(errno));
             continue;
         }