msm: kgsl: Add a terminating empty entry to a660_protected_regs array

The last entry of the a660_protected_regs array must be an empty
entry. The empty entry serves as a terminating placeholder value
indicating the end of the array.

Change-Id: Ie5dd6afcd65dca3ea1fa885d3aa675c23bdf5ca0
Signed-off-by: Raghu Ananya Arabolu <rarabolu@codeaurora.org>