thermal: Kconfig: cosmetic fixes

Fix typo, finish sentence and add missing dots.

Signed-off-by: Luka Perkov <luka@openwrt.org>
CC: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>