USB: usb-serial: call port_probe and port_remove at the right times

This patch (as1253) prevents the usb-serial core from calling a
driver's port_probe and port_remove methods more than once per port.
It also removes some unnecessary try_module_get() calls and adds a
missing port_remove method call in a failure path.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/usb/serial.h

@@ -27,6 +27,13 @@
 /* parity check flag */
 #define RELEVANT_IFLAG(iflag)	(iflag & (IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK))
 
+enum port_dev_state {
+	PORT_UNREGISTERED,
+	PORT_REGISTERING,
+	PORT_REGISTERED,
+	PORT_UNREGISTERING,
+};
+
 /**
  * usb_serial_port: structure for the specific ports of a device.
  * @serial: pointer back to the struct usb_serial owner of this port.
@@ -102,6 +109,7 @@ struct usb_serial_port {
 	char			console;
 	unsigned long		sysrq; /* sysrq timeout */
 	struct device		dev;
+	enum port_dev_state	dev_state;
 };
 #define to_usb_serial_port(d) container_of(d, struct usb_serial_port, dev)