mlxsw: i2c: Fix buffer increment counter for write transaction

It fixes a problem for the last chunk where 'chunk_size' is smaller than
MLXSW_I2C_BLK_MAX and data is copied to the wrong offset, overriding
previous data.

Fixes: 6882b0aee180 ("mlxsw: Introduce support for I2C bus")
Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/mellanox/mlxsw/i2c.c b/drivers/net/ethernet/mellanox/mlxsw/i2c.c
index 12c3a44..c0dcfa0 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/i2c.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/i2c.c
@@ -294,7 +294,7 @@
 		write_tran.len = MLXSW_I2C_ADDR_WIDTH + chunk_size;
 		mlxsw_i2c_set_slave_addr(tran_buf, off);
 		memcpy(&tran_buf[MLXSW_I2C_ADDR_BUF_SIZE], in_mbox +
-		       chunk_size * i, chunk_size);
+		       MLXSW_I2C_BLK_MAX * i, chunk_size);
 
 		j = 0;
 		end = jiffies + timeout;