ASoC: bf5xx-tdm-pcm: Staticize non exported struct

The bf5xx_tdm_pcm_ops struct is only used in bf5xx-tdm-pcm.c, so make it static.

Cc: Scott Jiang <scott.jiang.linux@gmail.com>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>