[otbn] Align error naming in call stack section of docs
Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/hw/ip/otbn/doc/_index.md b/hw/ip/otbn/doc/_index.md
index 23e8e36..f24f3ca 100644
--- a/hw/ip/otbn/doc/_index.md
+++ b/hw/ip/otbn/doc/_index.md
@@ -91,7 +91,7 @@
The call stack has a maximum depth of 8 elements.
Each instruction that reads from `x1` pops a single element from the stack.
Each instruction that writes to `x1` pushes a single element onto the stack.
-An instruction that reads from an empty stack or writes to a full stack causes OTBN to stop, raising an alert and setting the `ErrBitCallStack` bit in the {{< regref "ERR_BITS" >}} register.
+An instruction that reads from an empty stack or writes to a full stack causes a `CALL_STACK` [software error](#design-details-errors).
A single instruction can both read and write to the stack.
In this case, the read is ordered before the write.
