USB: serial: fix assumption that throttle/unthrottle cannot sleep

many serial subdrivers are clearly written as if throttle/unthrottle
cannot sleep. This leads to unneeded atomic submissions. This
patch converts affected drivers in a way to makes very clear that
throttle/unthrottle can sleep. Thus future misdesigns can be avoided
and efficiency and reliability improved.

This removes any such assumption using GFP_KERNEL and spin_lock_irq()

Signed-off-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/serial/empeg.c b/drivers/usb/serial/empeg.c
index 33c9e9c..7dd0e3e 100644
--- a/drivers/usb/serial/empeg.c
+++ b/drivers/usb/serial/empeg.c
@@ -391,7 +391,7 @@
 	dbg("%s - port %d", __func__, port->number);
 
 	port->read_urb->dev = port->serial->dev;
-	result = usb_submit_urb(port->read_urb, GFP_ATOMIC);
+	result = usb_submit_urb(port->read_urb, GFP_KERNEL);
 	if (result)
 		dev_err(&port->dev,
 			"%s - failed submitting read urb, error %d\n",