Fix typos

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/scripts/mbedtls_dev/bignum_mod.py b/scripts/mbedtls_dev/bignum_mod.py
index 6428873..25afe30 100644
--- a/scripts/mbedtls_dev/bignum_mod.py
+++ b/scripts/mbedtls_dev/bignum_mod.py
@@ -76,7 +76,7 @@
     arity = 1
     suffix = True
     disallow_zero_a = True
-    mongtomgery_form_a = True
+    montgomery_form_a = True
 
     def result(self) -> List[str]:
         result = bignum_common.invmod_positive(self.int_a, self.int_n)