Fix inverted assertion message

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/psa_crypto_slot_management.c b/library/psa_crypto_slot_management.c
index 2c4da78..1a54420 100644
--- a/library/psa_crypto_slot_management.c
+++ b/library/psa_crypto_slot_management.c
@@ -66,7 +66,7 @@
 
 MBEDTLS_STATIC_ASSERT(ARRAY_LENGTH(global_data.key_slots) <=
                       PSA_KEY_ID_VOLATILE_MAX - PSA_KEY_ID_VOLATILE_MIN + 1,
-                      "The volatile key range is larger than the key slot array");
+                      "The key slot array is larger than the volatile key ID range");
 
 int psa_is_valid_key_id(mbedtls_svc_key_id_t key, int vendor_ok)
 {