thermal: int340x: fix sparse warning

this patch fixes following sparse warning:

processor_thermal_device.c:188:6: warning: symbol 'proc_thermal_remove' was not declared. Should it be static?

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>