Add a way to link against different driver names.

The existing linker path hard-coded "-lRSDriver" into the command line, but
this won't work for partner drivers that have a different implementation
loaded. In order to still properly handle use of the CPU driver, this needs
to change depending on whether we actually loaded an OVERRIDE_RS_DRIVER or
not.

Change-Id: I0c4a4f12f5db819b234952bc8f364ac6300f147b
diff --git a/rsDriverLoader.cpp b/rsDriverLoader.cpp
index 37bd12a..528af0f 100644
--- a/rsDriverLoader.cpp
+++ b/rsDriverLoader.cpp
@@ -204,6 +204,9 @@
         goto error;
     }
 
+    // Only map in the actual driver name if we successfully load the runtime.
+    mDriverName = filename;
+
     return true;