Simplify the code with the new macros for PCM format type iterations.
This fixes the sparse warnings nicely:
  sound/core/pcm_native.c:2302:26: warning: restricted snd_pcm_format_t degrades to integer
  sound/core/pcm_native.c:2306:54: warning: incorrect type in argument 1 (different base types)
  sound/core/pcm_native.c:2306:54:    expected restricted snd_pcm_format_t [usertype] format
  sound/core/pcm_native.c:2306:54:    got unsigned int [assigned] k
  ....

No functional changes, just sparse warning fixes.

Link: https://lore.kernel.org/r/20200206163945.6797-6-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>