rtc: pcf2127: Fix typo in comment

Replace TFS2 with TSF2.

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211207215626.2619819-1-hugo@hugovil.com