udf: Export superblock magic to userspace

Currently UDF superblock magic doesn't appear in any userspace header
files and thus userspace apps have hard time checking for this fs. Let's
export the magic to userspace as with any other filesystem.
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/udf_sb.h

@@ -3,9 +3,7 @@
 
 #include <linux/mutex.h>
 #include <linux/bitops.h>
-
-/* Since UDF 2.01 is ISO 13346 based... */
-#define UDF_SUPER_MAGIC			0x15013346
+#include <linux/magic.h>
 
 #define UDF_MAX_READ_VERSION		0x0250
 #define UDF_MAX_WRITE_VERSION		0x0201

include/uapi/linux/magic.h

@@ -78,5 +78,7 @@
 #define BTRFS_TEST_MAGIC	0x73727279
 #define NSFS_MAGIC		0x6e736673
 #define BPF_FS_MAGIC		0xcafe4a11
+/* Since UDF 2.01 is ISO 13346 based... */
+#define UDF_SUPER_MAGIC		0x15013346
 
 #endif /* __LINUX_MAGIC_H__ */