ALSA: pcm: adaption of code formatting

This commit modifies current for readability in below aspects:
 - use bool type variable instead of int type variable assigned to 0/1
 - move variable definition from loop to top of the function definition

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>