USB: usblcd: drop redundant lcd mutex

Drop the redundant lcd mutex introduced by commit 925ce689 ("USB:
autoconvert trivial BKL users to private mutex") which replaced an
earlier BKL use.

The lock serialised calls to open() against other open() and a custom
ioctl() returning the bcdDevice (sic!), but neither is needed.
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20190926091228.24634-9-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/usblcd.c

@@ -30,7 +30,6 @@
 #define IOCTL_GET_DRV_VERSION	2
 
 
-static DEFINE_MUTEX(lcd_mutex);
 static const struct usb_device_id id_table[] = {
 	{ .idVendor = 0x10D2, .match_flags = USB_DEVICE_ID_MATCH_VENDOR, },
 	{ },
@@ -81,12 +80,10 @@ static int lcd_open(struct inode *inode, struct file *file)
 	struct usb_interface *interface;
 	int subminor, r;
 
-	mutex_lock(&lcd_mutex);
 	subminor = iminor(inode);
 
 	interface = usb_find_interface(&lcd_driver, subminor);
 	if (!interface) {
-		mutex_unlock(&lcd_mutex);
 		printk(KERN_ERR "USBLCD: %s - error, can't find device for minor %d\n",
 		       __func__, subminor);
 		return -ENODEV;
@@ -101,13 +98,11 @@ static int lcd_open(struct inode *inode, struct file *file)
 	r = usb_autopm_get_interface(interface);
 	if (r < 0) {
 		kref_put(&dev->kref, lcd_delete);
-		mutex_unlock(&lcd_mutex);
 		return r;
 	}
 
 	/* save our object in the file's private structure */
 	file->private_data = dev;
-	mutex_unlock(&lcd_mutex);
 
 	return 0;
 }
@@ -176,14 +171,12 @@ static long lcd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 	switch (cmd) {
 	case IOCTL_GET_HARD_VERSION:
-		mutex_lock(&lcd_mutex);
 		bcdDevice = le16_to_cpu((dev->udev)->descriptor.bcdDevice);
 		sprintf(buf, "%1d%1d.%1d%1d",
 			(bcdDevice & 0xF000)>>12,
 			(bcdDevice & 0xF00)>>8,
 			(bcdDevice & 0xF0)>>4,
 			(bcdDevice & 0xF));
-		mutex_unlock(&lcd_mutex);
 		if (copy_to_user((void __user *)arg, buf, strlen(buf)) != 0)
 			return -EFAULT;
 		break;