fstab: fix data encryption

In /dev/block/platform/msm_sdcc.1/by-name/, there is no metadata partition,
but there is an encrypt partition which is not used otherwise. Use the latter
in fstab.ls970 to store the encryption footer.

Change-Id: Ic0e1339342b33514dbb892ed2048763c43ce18fb
Merge branch 'cm-11.0' into kk_mkt