in_interrupt() is a pretty vague context description as it means: hard
interrupt, soft interrupt or bottom half disabled regions.

Replace the vague comment with a proper reasoning why spin_lock_irqsave()
needs to be used.

Signed-off-by: Ahmed S. Darwish <redacted>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <redacted>
Cc: Duncan Sands <duncan.sands@free.fr>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org

---
  drivers/usb/atm/usbatm.c |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/usb/atm/usbatm.c
+++ b/drivers/usb/atm/usbatm.c

@@ -249,7 +249,7 @@ static void usbatm_complete(struct urb *
  	/* vdbg("%s: urb 0x%p, status %d, actual_length %d",
  	     __func__, urb, status, urb->actual_length); */
  
-	/* usually in_interrupt(), but not always */
+	/* Can be invoked from task context, protect against interrupts */
  	spin_lock_irqsave(&channel->lock, flags);
  
  	/* must add to the back when receiving; doesn't matter when sending */