Don't depend on String8 cast to C string

Bug: 295394788
Test: m checkbuild
Change-Id: I6aa039b6b2a4944e3537ef133f8785890d957edd
diff --git a/tools/validatekeymaps/Main.cpp b/tools/validatekeymaps/Main.cpp
index 0d7d5f9..6cae3ec 100644
--- a/tools/validatekeymaps/Main.cpp
+++ b/tools/validatekeymaps/Main.cpp
@@ -165,7 +165,7 @@
 
         case FileType::INPUT_DEVICE_CONFIGURATION: {
             android::base::Result<std::unique_ptr<PropertyMap>> propertyMap =
-                    PropertyMap::load(String8(filename));
+                    PropertyMap::load(String8(filename).c_str());
             if (!propertyMap.ok()) {
                 error("Error %d parsing input device configuration file.\n\n",
                       propertyMap.error().code());