You are missing column assignment after ON DUPLICATE KEY UPDATE clause.
From MySQL manual:
13.2.5. INSERT Syntax
INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE]
[INTO] tbl_name [(col_name,...)]
{VALUES | VALUE} ({expr | DEFAULT},...),(...),...
[ ON DUPLICATE KEY UPDATE
col_name=expr
[, col_name=expr] ... ]
13.2.5. INSERT Syntax
13.2.5.3. INSERT ... ON DUPLICATE KEY UPDATE Syntax