ALSA: pcm: use helper functions to check whether parameters are determined

A commit 8bea869c ("ALSA: PCM midlevel: improve fifo_size handling")
allows drivers to implement calculation of fifo size in parameter
structure. This calculation runs only when two of the other parameters
have single value.

In ALSA PCM core, there're some helper functions for the case. This commit
applies the functions instead of value comparison.

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