char: lp: properly count the lp devices

When the parallel port is usb based and the lp attaches to it based on
LP_PARPORT_AUTO, we do get /dev/lp0 and when we remove the usb device
/dev/lp0 is unregistered. If we now reconnect the usb device we get
our /dev/lp0 back. But if we now disconnect and reconnect eight times
we donot get any lp device and dmesg shows:

    lp: ignoring parallel port (max. 8)

Decrement the lp_count when the device detaches as this represents the
number of lp devices connected to the system.
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/lp.c

@@ -993,6 +993,7 @@ static void lp_detach(struct parport *port)
 	for (n = 0; n < LP_NO; n++) {
 		if (port_num[n] == port->number) {
 			port_num[n] = -1;
+			lp_count--;
 			device_destroy(lp_class, MKDEV(LP_MAJOR, n));
 			parport_unregister_device(lp_table[n].dev);
 		}