udf: constify crc

- constify internal crc table
- mark udf_crc "in" parameter as const

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/udf/udfdecl.h b/fs/udf/udfdecl.h
index 2310b5c..26bc9c2 100644
--- a/fs/udf/udfdecl.h
+++ b/fs/udf/udfdecl.h
@@ -210,7 +210,7 @@
 extern short_ad *udf_get_fileshortad(uint8_t *, int, uint32_t *, int);
 
 /* crc.c */
-extern uint16_t udf_crc(uint8_t *, uint32_t, uint16_t);
+extern uint16_t udf_crc(const uint8_t *, uint32_t, uint16_t);
 
 /* udftime.c */
 extern time_t *udf_stamp_to_time(time_t *, long *, kernel_timestamp);