cm: Fix default notification sound

* Deneb.ogg was removed in a recent commit. Replace it with Argon.ogg
  which sounds exactly the same.

Change-Id: I8194ca5c9990dd80bbf07ed89965d4bf0b8070b6
Merge branch 'cm-10.1' of https://github.com/CyanogenMod/android_vendor_cm into linaro