ALSA: hda: Add missing sanity checks in PM prepare/complete callbacks

The recently added PM prepare and complete callbacks don't have the
sanity check whether the card instance has been properly initialized,
which may potentially lead to Oops.

This patch adds the azx_is_pm_ready() call in each place
appropriately like other PM callbacks.

Fixes: f5dac54d

 ("ALSA: hda: Separate runtime and system suspend")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210329113059.25035-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>