debugfs: Fix !DEBUG_FS debugfs_create_automount

If DEBUG_FS=n, compile fails with the following error:

kernel/trace/trace.c: In function 'tracing_init_dentry':
kernel/trace/trace.c:8658:9: error: passing argument 3 of 'debugfs_create_automount' from incompatible pointer type [-Werror=incompatible-pointer-types]
 8658 |         trace_automount, NULL);
      |         ^~~~~~~~~~~~~~~
      |         |
      |         struct vfsmount * (*)(struct dentry *, void *)
In file included from kernel/trace/trace.c:24:
./include/linux/debugfs.h:206:25: note: expected 'struct vfsmount * (*)(void *)' but argument is of type 'struct vfsmount * (*)(struct dentry *, void *)'
  206 |      struct vfsmount *(*f)(void *),
      |      ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~

Signed-off-by: Kusanagi Kouichi <slash@ac.auone-net.jp>
Link: https://lore.kernel.org/r/20191121102021787.MLMY.25002.ppp.dion.ne.jp@dmta0003.auone-net.jp


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>