leds: clevo-mail: fix Kconfig "its" grammar

Use the possessive "its" instead of the contraction "it's"
where appropriate.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: linux-leds@vger.kernel.org
Signed-off-by: Pavel Machek <pavel@ucw.cz>