mfd: tps80031: Add terminating entry for tps80031_id_table

The i2c_device_id table is supposed to be zero-terminated.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>