ALSA: sb: Proper endian notations

The data types defined in SB CSP driver code are all in little-endian,
hence the proper type like __le32 should be used.

Spotted by sparse, a warning like:
  sound/isa/sb/sb16_csp.c:330:14: warning: cast to restricted __le32

Signed-off-by: Takashi Iwai <tiwai@suse.de>