ARM64: dts: meson-axg: remove spdif out from gpio a7

Spdif out in not multiplexed on gpio A7 (spdif in is)
Remove this entry to fix the problem.

Fixes: 53c03b0aff36 ("ARM64: dts: meson-axg: add spdif output pins")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>