ALSA: mixart: Correct comment wrt obsoleted tasklet usage

The miXart driver has been already converted to use the threaded IRQ
instead of tasklet while there is a remaining comment still mentioning
a tasklet.  Update the comment appropriately.

Fixes: 8d3a8b5c ("ALSA: mixart: Use nonatomic PCM ops")
Link: https://lore.kernel.org/r/20200903104131.21097-12-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/mixart/mixart.h

@@ -69,7 +69,7 @@ struct mixart_mgr {
 	u32 msg_fifo[MSG_FIFO_SIZE];
 	int msg_fifo_readptr;
 	int msg_fifo_writeptr;
-	atomic_t msg_processed;       /* number of messages to be processed in tasklet */
+	atomic_t msg_processed;       /* number of messages to be processed in irq thread */
 
 	struct mutex lock;              /* interrupt lock */
 	struct mutex msg_lock;		/* mailbox lock */