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

include/linux/debugfs.h

@@ -54,6 +54,8 @@ static const struct file_operations __fops = {				\
 	.llseek  = no_llseek,						\
 }
 
+typedef struct vfsmount *(*debugfs_automount_t)(struct dentry *, void *);
+
 #if defined(CONFIG_DEBUG_FS)
 
 struct dentry *debugfs_lookup(const char *name, struct dentry *parent);
@@ -75,7 +77,6 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent);
 struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
 				      const char *dest);
 
-typedef struct vfsmount *(*debugfs_automount_t)(struct dentry *, void *);
 struct dentry *debugfs_create_automount(const char *name,
 					struct dentry *parent,
 					debugfs_automount_t f,
@@ -203,7 +204,7 @@ static inline struct dentry *debugfs_create_symlink(const char *name,
 
 static inline struct dentry *debugfs_create_automount(const char *name,
 					struct dentry *parent,
-					struct vfsmount *(*f)(void *),
+					debugfs_automount_t f,
 					void *data)
 {
 	return ERR_PTR(-ENODEV);