Fix typos

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/scripts/mbedtls_dev/bignum_common.py b/scripts/mbedtls_dev/bignum_common.py
index dd4fc36..c4efabf 100644
--- a/scripts/mbedtls_dev/bignum_common.py
+++ b/scripts/mbedtls_dev/bignum_common.py
@@ -249,7 +249,7 @@
     #pylint: disable=abstract-method
     """Target for bignum mod_raw test case generation."""
     moduli = MODULI_DEFAULT # type: List[str]
-    mongtomgery_form_a = False
+    montgomery_form_a = False
     disallow_zero_a = False
 
     def __init__(self, val_n: str, val_a: str, val_b: str = "0",
@@ -272,7 +272,7 @@
 
     @property
     def arg_a(self) -> str:
-        if self.mongtomgery_form_a:
+        if self.montgomery_form_a:
             value_a = self.to_montgomery(self.int_a)
         else:
             value_a = self.int_a