manifest: track busybox from OmniROM

busybox is used in twrp. twrp comes from omni.
It only makes sense to track busybox from
the same place as our recovery.

Change-Id: I671c1949e779bb0088d861a4876d1adebd79cd9b
Signed-off-by: Simon Sickle <simon@simonsickle.com>