samples: i2s_codec: Fix i2s API misuse

Replace i2s_write invocation with i2s_buf_write invocation for test sine
wave playback.

When CONFIG_USE_DMIC=n, this sample attempts to play back a test sine
wave encoded in sine.h. As the i2s_write treats the given buffer as a
memory slab, it overwrites parts of it, resulting in data corruption and
improper playback. i2s_buf_write accepts a buffer existing outside the
playback queue (heap).

Manually tested on mimxrt595_evk/mimxrt595s/cm33 where it was first
observed.

Signed-off-by: Vit Stanicek <vit.stanicek@nxp.com>