ASoC: 88pm860x-codec: Fix possibly missing string termination

Coverity spotted an issue with strncpy() in pm860x_codec_probe()
which does not take the \0 termination byte into account. Fix this
by making the buffers one byte larger so the can really accommodate
MAX_NAME_LEN bytes long strings.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Mark Brown <broonie@kernel.org>