Fix typo

Signed-off-by: Ryan Everett <ryan.everett@arm.com>
diff --git a/library/threading.c b/library/threading.c
index 94404ac..c28290f 100644
--- a/library/threading.c
+++ b/library/threading.c
@@ -149,7 +149,7 @@
     mbedtls_mutex_init(&mbedtls_threading_gmtime_mutex);
 #endif
 #if defined(MBEDTLS_PSA_CRYPTO_C)
-    mbedtls_mutext_init(&mbedtls_threading_key_slot_mutex);
+    mbedtls_mutex_init(&mbedtls_threading_key_slot_mutex);
 #endif
 }