pinctrl: meson: meson8b: fix the sdxc_a data 1..3 pins

Fix the mismatch between the "sdxc_d13_1_a" pin group definition from
meson8b_cbus_groups and the entry in sdxc_a_groups ("sdxc_d0_13_1_a").
This makes it possible to use "sdxc_d13_1_a" in device-tree files to
route the MMC data 1..3 pins to GPIOX_1..3.

Fixes: 0fefcb68 ("pinctrl: Add support for Meson8b")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>