staging: unisys: visorbus: add missing include

this removes lots of sparse warnings :
warning: symbol 'visorchannel_destroy' was not declared. Should it be static?
warning: symbol 'visorchannel_get_physaddr' was not declared. Should it be static?
warning: symbol 'visorchannel_get_nbytes' was not declared. Should it be static?
warning: symbol 'visorchannel_uuid_id' was not declared. Should it be static?
warning: symbol 'visorchannel_id' was not declared. Should it be static?
warning: symbol 'visorchannel_zoneid' was not declared. Should it be static?
warning: symbol 'visorchannel_get_clientpartition' was not declared. Should it be static?
warning: symbol 'visorchannel_set_clientpartition' was not declared. Should it be static?
warning: symbol 'visorchannel_read' was not declared. Should it be static?
warning: symbol 'visorchannel_write' was not declared. Should it be static?
warning: symbol 'visorchannel_get_header' was not declared. Should it be static?
warning: symbol 'visorchannel_create' was not declared. Should it be static?
warning: symbol 'visorchannel_create_with_lock' was not declared. Should it be static?

Signed-off-by: Laurent Navet <laurent.navet@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/unisys/visorbus/visorchannel.c

@@ -23,6 +23,7 @@
 #include <linux/io.h>
 
 #include "visorbus.h"
+#include "visorbus_private.h"
 #include "controlvmchannel.h"
 
 #define MYDRVNAME "visorchannel"