ALSA: echoaudio: Proper endian notations

Many data fields defined in echoaudio drivers are in little-endian,
hence they should be defined with __le16 or __le32.  This makes it
easier to catch the forgotten conversions.

Spotted by sparse, a warning like:
  sound/pci/echoaudio/echoaudio_dsp.c:990:36: warning: incorrect type in assignment (different base types)

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