fsnotify: move declaration of fsnotify_mark_connector_cachep to fsnotify.h

Move fsnotify_mark_connector_cachep to fsnotify.h to properly
share it with the user in mark.c and avoid the following warning
from sparse:

fs/notify/mark.c:82:19: warning: symbol 'fsnotify_mark_connector_cachep' was not declared. Should it be static?

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ben Dooks <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/notify/fsnotify.c

···
 }
 EXPORT_SYMBOL_GPL(fsnotify);
 
-extern struct kmem_cache *fsnotify_mark_connector_cachep;
-
 static __init int fsnotify_init(void)
 {
 	int ret;

fs/notify/fsnotify.h

···
 extern struct fsnotify_event_holder *fsnotify_alloc_event_holder(void);
 extern void fsnotify_destroy_event_holder(struct fsnotify_event_holder *holder);
 
+extern struct kmem_cache *fsnotify_mark_connector_cachep;
+
 #endif	/* __FS_NOTIFY_FSNOTIFY_H_ */