drivers: thermal: Avoid section mismatch

Thermal drivers netlink init section is calling driver cleanup
function in the exit section. This will cause a section mismatch.

Remove the clean up function from exit section to avoid section mismatch.

Change-Id: Id04b1ace0c50fe74989071564d52f7b635980eb7
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>