msm: thermal: Fix zone id to tsens map lookup

Fix null pointer dereference due to non-initialization
of tsens lookup table.

If tsens map lookup table is not initialized, assign
zone_id to tsens_id.

Change-Id: I911bcc2527bd8e00462f7428d8dead4286368fa1
Acked-by: Jim Granitzki <jamesg@qti.qualcomm.com>
Signed-off-by: Kranthikumar Kurapati <kkurap@codeaurora.org>