debugfs: debugfs_use_start/finish do not exist anymore

debugfs_use_file_start() and debugfs_use_file_finish() do not exist
since commit c9afbec27089 ("debugfs: purge obsolete SRCU based removal
protection"); tweak debugfs_create_file_unsafe() comment.

Signed-off-by: Sergey Senozhatsky <[e-mail]>
Reviewed-by: Rafael J. Wysocki <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

fs/debugfs/inode.c

···
  * debugfs core.
  *
  * It is your responsibility to protect your struct file_operation
- * methods against file removals by means of debugfs_use_file_start()
- * and debugfs_use_file_finish(). ->open() is still protected by
+ * methods against file removals by means of debugfs_file_get()
+ * and debugfs_file_put(). ->open() is still protected by
  * debugfs though.
  *
  * Any struct file_operations defined by means of