mfd: tps65218: Fix trivial typo in comment

The driver is for TPS65218, not TPS65219.

Signed-off-by: Daniel Ammann <daniel.ammann@bytesatwork.ch>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220405125426.28016-1-daniel.ammann@bytesatwork.ch