[otbn] Add missing asserts for illegal bus access error

In #7626 we added a new fatal error, but I didn't update the static
asserts in the two software libraries. Rectify that.

Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/sw/device/lib/dif/dif_otbn.c b/sw/device/lib/dif/dif_otbn.c
index e50d290..d8485ed 100644
--- a/sw/device/lib/dif/dif_otbn.c
+++ b/sw/device/lib/dif/dif_otbn.c
@@ -29,6 +29,9 @@
               "Layout of error bits changed.");
 static_assert(kDifOtbnErrBitsFatalReg == (1 << OTBN_ERR_BITS_FATAL_REG_BIT),
               "Layout of error bits changed.");
+static_assert(kDifOtbnErrBitsFatalIllegalBusAccess ==
+                  (1 << OTBN_ERR_BITS_FATAL_ILLEGAL_BUS_ACCESS_BIT),
+              "Layout of error bits changed.");
 
 /**
  * Data width of big number subset, in bytes.
diff --git a/sw/device/silicon_creator/lib/drivers/otbn.c b/sw/device/silicon_creator/lib/drivers/otbn.c
index f7e4968..095b08d 100644
--- a/sw/device/silicon_creator/lib/drivers/otbn.c
+++ b/sw/device/silicon_creator/lib/drivers/otbn.c
@@ -27,6 +27,8 @@
 ASSERT_ERR_BIT_MATCH(kOtbnErrBitsFatalImem, OTBN_ERR_BITS_FATAL_IMEM_BIT);
 ASSERT_ERR_BIT_MATCH(kOtbnErrBitsFatalDmem, OTBN_ERR_BITS_FATAL_DMEM_BIT);
 ASSERT_ERR_BIT_MATCH(kOtbnErrBitsFatalReg, OTBN_ERR_BITS_FATAL_REG_BIT);
+ASSERT_ERR_BIT_MATCH(kOtbnErrBitsFatalIllegalBusAccess,
+                     OTBN_ERR_BITS_FATAL_ILLEGAL_BUS_ACCESS_BIT);
 
 const size_t kOtbnDMemSizeBytes = OTBN_DMEM_SIZE_BYTES;
 const size_t kOtbnIMemSizeBytes = OTBN_IMEM_SIZE_BYTES;