ALSA: opl4 - Fix a wrong argument in proc write callback

The commit 24e4a1211f691fc671de44685430dbad757d8487
    ALSA: info - Use standard types for info callbacks
introduced a wrong type to snd_opl4_mem_proc_write() for pos argument.
Fixed now.

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

sound/drivers/opl4/opl4_proc.c

@@ -73,7 +73,7 @@ static ssize_t snd_opl4_mem_proc_write(struct snd_info_entry *entry,
 				       void *file_private_data,
 				       struct file *file,
 				       const char __user *_buf,
-				       size_t count, size_t pos)
+				       size_t count, loff_t pos)
 {
 	struct snd_opl4 *opl4 = entry->private_data;
 	char *buf;