MediaCas: move clear key plugin to /system/lib

Non-treble process can no longer load .so from /vendor/lib.
Move the clear key plugin to /system/lib until MediaCas is converted
to treble.

bug: 37476803
Change-Id: I563b4576aeada5470355e7e168fa2c73997004d7
diff --git a/services/mediadrm/FactoryLoader.h b/services/mediadrm/FactoryLoader.h
index 1e03e9b..d7f1118 100644
--- a/services/mediadrm/FactoryLoader.h
+++ b/services/mediadrm/FactoryLoader.h
@@ -88,7 +88,7 @@
     }
 
     // no luck, have to search
-    String8 dirPath("/vendor/lib/mediacas");
+    String8 dirPath("/system/lib/mediacas");
     DIR* pDir = opendir(dirPath.string());
 
     if (pDir == NULL) {
@@ -123,7 +123,7 @@
 
     results->clear();
 
-    String8 dirPath("/vendor/lib/mediacas");
+    String8 dirPath("/system/lib/mediacas");
     DIR* pDir = opendir(dirPath.string());
 
     if (pDir == NULL) {