ThemesProvider: Fix query compilation error

This fixes syntax error when excute the SELECT Clause

06-11 13:45:39.370: E/AndroidRuntime(3359): java.lang.RuntimeException: Unable to start
receiver org.cyanogenmod.themes.provider.AppReceiver: android.database.sqlite.SQLiteException:
near "?": syntax error (code 1): , while compiling: SELECT pkg_name FROM themes WHERE (pkg_name?)

Change-Id: If9857b1db447e8752ddf04ce3f7d2cc84d5b28a5