staging: gpib: Add missing mutex unlock in ni usb driver

When the buffer allocation for return data in ni_usb_write() fails
we were returning without unlocking the addressed_transfer_lock.

Add the unlock call.

This was detected by smatch:
New smatch warnings:
drivers/staging/gpib/ni_usb/ni_usb_gpib.c:837 ni_usb_write() warn: inconsistent returns '&ni_priv->addressed_transfer_lock'.

Reported-by: kernel test robot <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]/
Signed-off-by: Dave Penkler <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: dpenkler

drivers/staging/gpib/ni_usb/ni_usb_gpib.c

@@ -783,8 +783,10 @@ static int ni_usb_write(gpib_board_t *board, uint8_t *buffer, size_t length,
 	}
 
 	in_data = kmalloc(in_data_length, GFP_KERNEL);
-	if (!in_data)
+	if (!in_data) {
+		mutex_unlock(&ni_priv->addressed_transfer_lock);
 		return -ENOMEM;
+	}
 	retval = ni_usb_receive_bulk_msg(ni_priv, in_data, in_data_length, &usb_bytes_read,
 					 ni_usb_timeout_msecs(board->usec_timeout), 1);