afs: Fix the afs_uuid struct to make the char-sized fields signed

In AFS's encoding of a UUID, the eight 'char' fields are all signed, so
represent them with __s8 rather than __u8.  This makes the compiler
sign-extend them correctly when XDR-encoding them.
Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/afs.h

@@ -79,9 +79,9 @@ struct afs_uuid {
 	__be32		time_low;			/* low part of timestamp */
 	__be16		time_mid;			/* mid part of timestamp */
 	__be16		time_hi_and_version;		/* high part of timestamp and version  */
-	__u8		clock_seq_hi_and_reserved;	/* clock seq hi and variant */
-	__u8		clock_seq_low;			/* clock seq low */
-	__u8		node[6];			/* spatially unique node ID (MAC addr) */
+	__s8		clock_seq_hi_and_reserved;	/* clock seq hi and variant */
+	__s8		clock_seq_low;			/* clock seq low */
+	__s8		node[6];			/* spatially unique node ID (MAC addr) */
 };
 
 /*