init.d: 03_zram_tonyp: Do not execute the script if there is already a zram device

See: https://github.com/tonyp/android_vendor_cm/commit/53ad5a6161a815405caa3634083cb42c20f7f0a5#commitcomment-6461227
Merge pull request #1 from Firtecy/cm-11.0-tonyp

init.d: 03_zram_tonyp: Do not execute the script if there is already a z...