ASoC: Intel: avs: correct config reference for I2S test board

Commit e39acc4c ("ASoC: Intel: avs: Add I2S-test machine board") adds
the config "SND_SOC_INTEL_AVS_MACH_I2S_TEST", but in the Makefile refers
to  config "SND_SOC_INTEL_AVS_MACH_i2s_TEST" (notice the uppercase and
lowercase difference).

Adjust the Makefile to refer to the actual existing config.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Cezary Rojewski <cezary.rojewski@intel.com>
Reviewed-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Link: https://lore.kernel.org/r/20220705103238.7484-1-lukas.bulwahn@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>