Address const issues in preparation for libcxx rebase.

Change-Id: I4eccc1b5a70da9dd325e1a7e10ab0a3fe588c03f
diff --git a/adb/socket_test.cpp b/adb/socket_test.cpp
index 5cbef6d..20a3bbb 100644
--- a/adb/socket_test.cpp
+++ b/adb/socket_test.cpp
@@ -275,8 +275,8 @@
 
 // Checks that skip_host_serial(serial) returns a pointer to the part of |serial| which matches
 // |expected|, otherwise logs the failure to gtest.
-void VerifySkipHostSerial(const std::string& serial, const char* expected) {
-    const char* result = internal::skip_host_serial(serial.c_str());
+void VerifySkipHostSerial(std::string serial, const char* expected) {
+    char* result = internal::skip_host_serial(&serial[0]);
     if (expected == nullptr) {
         EXPECT_EQ(nullptr, result);
     } else {