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>

drivers/leds/Kconfig

@@ -456,7 +456,7 @@ config LEDS_CLEVO_MAIL
 
 	  The driver supports two kinds of interface: using ledtrig-timer
 	  or through /sys/class/leds/clevo::mail/brightness. As this LED
-	  cannot change it's brightness it blinks instead. The brightness
+	  cannot change its brightness it blinks instead. The brightness
 	  value 0 means off, 1..127 means blink at 0.5Hz and 128..255 means
 	  blink at 1Hz.