ARM: dts: msm: Correct mixer offsets for sdm670

Not all the SDE layer mixer HW block offsets are valid for a given
target device. All the valid mixer HW block id's need not be
contiguous for a device. This change populates the offset value
as 0 for invalid layer mixer blocks in a non-contiguous scenario.
This helps SDE HW catalog to keep track of actual LM count.

Change-Id: Ieea74bba7453dd08f34b2731353f4fb1d34a99e1
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>