thermal: tsens: Add NULL pointer check for id

Add NULL pointer check for id value to avoid the
NULL pointer dereference when of_match_node function
can return NULL for non-matching node.

Change-Id: If01290f11c44631249b0740271b2d51a3654b54a
Signed-off-by: Dipen Parmar <dipenp@codeaurora.org>