thermal: Fix potential NULL pointer accesses

The type parameter in thermal_zone_device_register and
thermal_cooling_device_register can be NULL, indicating that no sysfs attribute
for the type should be created. Only call strlen() and strcpy() on type if it is
not NULL.

This patch addresses Coverity #102180 and #102182: Dereference before null check

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>