USB: cdc-acm: clean up throttle handling

Clean up the throttle implementation by dropping the redundant
throttle_req flag which was a remnant from back when USB serial had only
a single read URB, something which was later carried over to cdc-acm.

Also convert the throttled flag to an atomic bit flag.

Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-acm.h

@@ -108,6 +108,7 @@ struct acm {
 	unsigned long flags;
 #		define EVENT_TTY_WAKEUP	0
 #		define EVENT_RX_STALL	1
+#		define ACM_THROTTLED	2
 	struct usb_cdc_line_coding line;		/* bits, stop, parity */
 	struct work_struct work;			/* work queue entry for line discipline waking up */
 	unsigned int ctrlin;				/* input control lines (DCD, DSR, RI, break, overruns) */
@@ -122,8 +123,6 @@ struct acm {
 	unsigned int ctrl_caps;				/* control capabilities from the class specific header */
 	unsigned int susp_count;			/* number of suspended interfaces */
 	unsigned int combined_interfaces:1;		/* control and data collapsed */
-	unsigned int throttled:1;			/* actually throttled */
-	unsigned int throttle_req:1;			/* throttle requested */
 	u8 bInterval;
 	struct usb_anchor delayed;			/* writes queued for a device about to be woken */
 	unsigned long quirks;