thermal: core: fix some format issues on critical shutdown string

The critical shutdown notice string used to have some spaces missing,
which makes it not so pretty.

Add the spaces to satisfy usual English space rules.

Reported-by: Mingcong Bai <jeffbai@aosc.io>
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>