ASoC: meson: axg-card: remove useless check on codec

While checking cpus before dereferencing the pointer is required, it is
not necessary for codecs. 'codec' can't possibly be NULL in the loop

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>