pinctrl: meson-axg: adjust spicc pin naming

According to datasheet, we should use numbers for the pin naming
instead of letters. The patch here try to fix this to keep
the consistency.

This patch should not bring any functional change.

Fixes: 83c56680 ("pinctrl: meson-axg: Add new pinctrl driver for Meson AXG SoC")
Suggested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>