autofs: Only declare function when CONFIG_COMPAT is defined

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

fs/autofs/root.c:30: warning: ‘autofs_root_compat_ioctl’ declared ‘static’ but never defined
Signed-off-by: NMárton Németh <nm127@freemail.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>

fs/autofs/root.c

@@ -27,7 +27,9 @@ static int autofs_root_unlink(struct inode *,struct dentry *);
 static int autofs_root_rmdir(struct inode *,struct dentry *);
 static int autofs_root_mkdir(struct inode *,struct dentry *,int);
 static long autofs_root_ioctl(struct file *,unsigned int,unsigned long);
+#ifdef CONFIG_COMPAT
 static long autofs_root_compat_ioctl(struct file *,unsigned int,unsigned long);
+#endif
 
 const struct file_operations autofs_root_operations = {
 	.llseek		= generic_file_llseek,