Use String8/16 c_str [drm]

Bug: 295394788
Test: make checkbuild
Change-Id: I8446de3a553a3ddce2da5c4551127039638e0a98
diff --git a/drm/1.0/default/DrmPlugin.cpp b/drm/1.0/default/DrmPlugin.cpp
index 809f694..dfa5d22 100644
--- a/drm/1.0/default/DrmPlugin.cpp
+++ b/drm/1.0/default/DrmPlugin.cpp
@@ -98,8 +98,7 @@
                 break;
             }
         }
-        _hidl_cb(toStatus(status), toHidlVec(legacyRequest), requestType,
-                 defaultUrl.string());
+        _hidl_cb(toStatus(status), toHidlVec(legacyRequest), requestType, defaultUrl.c_str());
         return Void();
     }
 
@@ -219,7 +218,7 @@
         String8 legacyValue;
         status_t status = mLegacyPlugin->getPropertyString(
                 String8(propertyName.c_str()), legacyValue);
-        _hidl_cb(toStatus(status), legacyValue.string());
+        _hidl_cb(toStatus(status), legacyValue.c_str());
         return Void();
     }