tty: ipwireless: remove unused ipw_dev::attribute_memory

clang-struct [1] found ipw_dev::attribute_memory unused.

As far as I can see it was never used since the driver merge. Drop it.

[1] https://github.com/jirislaby/clang-structSigned-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: David Sterba <dsterba@suse.com>
Acked-by: David Sterba <dsterba@suse.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20231121103626.17772-3-jirislaby@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/ipwireless/main.h

@@ -49,9 +49,6 @@ struct ipw_dev {
 
 	void __iomem *common_memory;
 
-	/* Reference to attribute memory, containing CIS data */
-	void *attribute_memory;
-
 	/* Hardware context */
 	struct ipw_hardware *hardware;
 	/* Network layer context */