ASoC: mediatek: mt8186: remove unnecessary NULL check

The "i2s_priv" pointer cannot be NULL.  Some NULL checks were deleted
in commit d7bffbe9 ("ASoC: mediatek: mt8186: remove unnecessary
judgments") but this one was accidentally left behind.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/Yuo7LGPk8KnBW6ac@kili


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