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/keyspan_pda.c b/drivers/usb/serial/keyspan_pda.c
index 257c16c..1296a09 100644
--- a/drivers/usb/serial/keyspan_pda.c
+++ b/drivers/usb/serial/keyspan_pda.c
@@ -290,7 +290,7 @@
 	/* just restart the receive interrupt URB */
 	dbg("keyspan_pda_rx_unthrottle port %d", port->number);
 	port->interrupt_in_urb->dev = port->serial->dev;
-	if (usb_submit_urb(port->interrupt_in_urb, GFP_ATOMIC))
+	if (usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL))
 		dbg(" usb_submit_urb(read urb) failed");
 	return;
 }