ALSA: fm801: put curly braces around empty if-body

The compiler complains on unused condition as follows

sound/pci/fm801.c: In function ‘snd_fm801_interrupt’:
sound/pci/fm801.c:585:3: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body]

Put the curly braces around empty body as suggested.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/pci/fm801.c

@@ -592,8 +592,9 @@ static irqreturn_t snd_fm801_interrupt(int irq, void *dev_id)
 	}
 	if (chip->rmidi && (status & FM801_IRQ_MPU))
 		snd_mpu401_uart_interrupt(irq, chip->rmidi->private_data);
-	if (status & FM801_IRQ_VOLUME)
-		;/* TODO */
+	if (status & FM801_IRQ_VOLUME) {
+		/* TODO */
+	}
 
 	return IRQ_HANDLED;
 }