net: usb: net1080: Remove in_interrupt() comment

The comment above nc_vendor_write() suggests that the function could become
async so that is usable in `in_interrupt()' context or that it already is
safe to be called from such a context.

Eitherway: The function did not become async since v2.4.9.2 (2002) and it
must be not be called from `in_interrupt()' context because it sleeps on
mutltiple occations.

Remove the misleading comment.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>