ASoC: tegra: Fix unused variable 'spdif' warning

Fix below build warning:
  CC [M]  sound/soc/tegra/tegra20_spdif.o
sound/soc/tegra/tegra20_spdif.c: In function 'tegra20_spdif_platform_remove':
sound/soc/tegra/tegra20_spdif.c:361:24: warning: unused variable 'spdif' [-Wunused-variable]

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>