You seem to be using an old OpenOCD. Line 202 of that script is different now.
https://github.com/openocd-org/openocd/blob/1998b1e5a89e57b2d1109bc36d6af916106103ff/tcl/target/stm32h7x.cfg#L202 You should try the latest 0.12.0 release or even a build from the head of the source repository.
