[ALSA] Fix rwlock around snd_iprintf() in sound core

Fixed rwlock around snd_iprintf() in sound core part.
Replaced with mutex.
Also, make mutex and flags static variables with addition of
snd_card_locked() function (just for sound.c).

Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/sound.c

diff --git a/sound/core/sound.c b/sound/core/sound.c
index 8313f97..02c8cc4 100644
--- a/sound/core/sound.c
+++ b/sound/core/sound.c
@@ -81,14 +81,9 @@
  */
 void snd_request_card(int card)
 {
-	int locked;
-
 	if (! current->fs->root)
 		return;
-	read_lock(&snd_card_rwlock);
-	locked = snd_cards_lock & (1 << card);
-	read_unlock(&snd_card_rwlock);
-	if (locked)
+	if (snd_card_locked(card))
 		return;
 	if (card < 0 || card >= cards_limit)
 		return;