ASoC: Intel: bxt-da7219-max98357a: return -EINVAL on unrecognized speaker amplifier

Currently if the ctx->spkamp is not recognized an error message is
reported but the code continues to set up the device with uninitialized
variables such as the number of widgets.  Fix this by returning -EINVAL
for unrecognized speaker amplifier types.

Fixes: e1435a1f

 ("ASoC: Intel: bxt-da7219-max98357a: support MAX98390 speaker amp")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Addresses-Coverity: ("Uninitialized scalar variable")
Link: https://lore.kernel.org/r/20200702114835.37889-1-colin.king@canonical.com
Signed-off-by: Mark Brown <broonie@kernel.org>