ALSA: pcm: Clean up SNDRV_PCM_IOCTL_PAUSE code

Use snd_pcm_action_lock_irq() helper instead of open coding.
No functional change.

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