ASoC: SOF: Intel: Fix unused variable warning

When CONFIG_SND_SOC_SOF_BAYTRAIL is not set, gcc warns:

sound/soc/sof/intel/byt.c:85:41: warning: ‘cht_debugfs’ defined but not used [-Wunused-const-variable=]
 static const struct snd_sof_debugfs_map cht_debugfs[] = {
                                         ^~~~~~~~~~~
Move the variable inside #ifdef

Reported-by: Hulk Robot <hulkci@huawei.com>
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20200507072735.16588-1-yuehaibing@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>