pinctrl: Fix an error in pin-function table of SP7021

The first valid item of pin-function table should
start from the third item. The first two items,
due to historical and compatible reasons, should
be dummy items.

The two dummy items were removed accidentally in
initial submission. This fix adds them back.

Signed-off-by: Wells Lu <wellslutw@gmail.com>
Link: https://lore.kernel.org/r/1650015688-19774-1-git-send-email-wellslutw@gmail.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>