ASoC: fsl: use strncpy() to prevent copying of over-long names

Use strncpy() instead of strcpy(). That's not a security issue, as the
source buffer is taken from DT nodes, but we should still enforce bound
checks. Spotted by Coverity.

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