Use String8/16 c_str [cas]

Bug: 295394788
Test: make checkbuild
Change-Id: I1faccac8711d5cccee70443548940d99804c7c2a
diff --git a/cas/aidl/default/FactoryLoader.h b/cas/aidl/default/FactoryLoader.h
index 6a562f6..0767607 100644
--- a/cas/aidl/default/FactoryLoader.h
+++ b/cas/aidl/default/FactoryLoader.h
@@ -86,10 +86,10 @@
 #else
     String8 dirPath("/vendor/lib/mediacas");
 #endif
-    DIR* pDir = opendir(dirPath.string());
+    DIR* pDir = opendir(dirPath.c_str());
 
     if (pDir == NULL) {
-        ALOGE("Failed to open plugin directory %s", dirPath.string());
+        ALOGE("Failed to open plugin directory %s", dirPath.c_str());
         return false;
     }
 
@@ -123,10 +123,10 @@
 #else
     String8 dirPath("/vendor/lib/mediacas");
 #endif
-    DIR* pDir = opendir(dirPath.string());
+    DIR* pDir = opendir(dirPath.c_str());
 
     if (pDir == NULL) {
-        ALOGE("Failed to open plugin directory %s", dirPath.string());
+        ALOGE("Failed to open plugin directory %s", dirPath.c_str());
         return false;
     }