ASoC: sti: uniperif: fix 'defined by not used' warning

Fix W=1 warning. The table uni_tdm_hw is declared in a header included
by multiple C file. This isn't really a good practice but for now
using __maybe_unused makes the following warning go away.

sound/soc/sti/sti_uniperif.c:12:
sound/soc/sti/uniperif.h:1351:38: warning: ‘uni_tdm_hw’ defined but
not used [-Wunused-const-variable=]
 1351 | static const struct snd_pcm_hardware uni_tdm_hw = {
      |                                      ^~~~~~~~~~
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Link: https://lore.kernel.org/r/20200709162328.259586-2-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sti/uniperif.h

@@ -1348,7 +1348,7 @@ struct sti_uniperiph_data {
 	struct sti_uniperiph_dai dai_data;
 };
 
-static const struct snd_pcm_hardware uni_tdm_hw = {
+static __maybe_unused const struct snd_pcm_hardware uni_tdm_hw = {
 	.info = SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER |
 		SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_MMAP |
 		SNDRV_PCM_INFO_MMAP_VALID,