erofs: on-disk format should have explicitly assigned numbers

As Christoph suggested [1], on-disk format should have
explicitly assigned numbers.

[1] https://lore.kernel.org/r/20190829095954.GB20598@infradead.org/Reported-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NGao Xiang <gaoxiang25@huawei.com>
Link: https://lore.kernel.org/r/20190904020912.63925-3-gaoxiang25@huawei.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/erofs/erofs_fs.h

@@ -53,10 +53,10 @@ struct erofs_super_block {
  * 4~7 - reserved
  */
 enum {
-	EROFS_INODE_FLAT_PLAIN,
-	EROFS_INODE_FLAT_COMPRESSION_LEGACY,
-	EROFS_INODE_FLAT_INLINE,
-	EROFS_INODE_FLAT_COMPRESSION,
+	EROFS_INODE_FLAT_PLAIN			= 0,
+	EROFS_INODE_FLAT_COMPRESSION_LEGACY	= 1,
+	EROFS_INODE_FLAT_INLINE			= 2,
+	EROFS_INODE_FLAT_COMPRESSION		= 3,
 	EROFS_INODE_LAYOUT_MAX
 };
 
@@ -184,7 +184,7 @@ struct erofs_xattr_entry {
 
 /* available compression algorithm types */
 enum {
-	Z_EROFS_COMPRESSION_LZ4,
+	Z_EROFS_COMPRESSION_LZ4	= 0,
 	Z_EROFS_COMPRESSION_MAX
 };
 
@@ -242,10 +242,10 @@ struct z_erofs_map_header {
  *                (di_advise could be 0, 1 or 2)
  */
 enum {
-	Z_EROFS_VLE_CLUSTER_TYPE_PLAIN,
-	Z_EROFS_VLE_CLUSTER_TYPE_HEAD,
-	Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD,
-	Z_EROFS_VLE_CLUSTER_TYPE_RESERVED,
+	Z_EROFS_VLE_CLUSTER_TYPE_PLAIN		= 0,
+	Z_EROFS_VLE_CLUSTER_TYPE_HEAD		= 1,
+	Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD	= 2,
+	Z_EROFS_VLE_CLUSTER_TYPE_RESERVED	= 3,
 	Z_EROFS_VLE_CLUSTER_TYPE_MAX
 };