thunderbolt: property: Fix a NULL pointer dereference

commit 106204b5

 upstream.

In case kzalloc fails, the fix releases resources and returns
-ENOMEM to avoid the NULL pointer dereference.

Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>