thermal: intel: quark_dts: fix error pointer dereference

If alloc_soc_dts() fails, then we can just return.  Trying to free
"soc_dts" will lead to an Oops.

Fixes: 8c187693

 ("thermal: intel Quark SoC X1000 DTS thermal driver")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>