Fix additional mis-spellings

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/tests/include/test/psa_exercise_key.h b/tests/include/test/psa_exercise_key.h
index e67f515..4306c1a 100644
--- a/tests/include/test/psa_exercise_key.h
+++ b/tests/include/test/psa_exercise_key.h
@@ -81,7 +81,7 @@
 #elif defined(MBEDTLS_SHA512_C)
 #define KNOWN_MBEDTLS_SUPPORTED_HASH_ALG PSA_ALG_SHA_512
 #else
-#undef KNOWN_MBEDLTS_SUPPORTED_HASH_ALG
+#undef KNOWN_MBEDTLS_SUPPORTED_HASH_ALG
 #endif
 
 /** \def KNOWN_SUPPORTED_BLOCK_CIPHER