autofs4: Only declare function when CONFIG_COMPAT is defined

The patch solves the following warnings message when CONFIG_COMPAT
is not defined:

fs/autofs4/root.c:31: warning: ‘autofs4_root_compat_ioctl’ declared ‘static’ but never defined

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Cc: Ian Kent <raven@themaw.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

fs/autofs4/root.c

@@ -28,7 +28,9 @@ static int autofs4_dir_unlink(struct inode *,struct dentry *);
 static int autofs4_dir_rmdir(struct inode *,struct dentry *);
 static int autofs4_dir_mkdir(struct inode *,struct dentry *,int);
 static long autofs4_root_ioctl(struct file *,unsigned int,unsigned long);
+#ifdef CONFIG_COMPAT
 static long autofs4_root_compat_ioctl(struct file *,unsigned int,unsigned long);
+#endif
 static int autofs4_dir_open(struct inode *inode, struct file *file);
 static struct dentry *autofs4_lookup(struct inode *,struct dentry *, struct nameidata *);
 static void *autofs4_follow_link(struct dentry *, struct nameidata *);