Fix cleanup code

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/programs/psa/hmac_md_psa.c b/programs/psa/hmac_md_psa.c
index 003fb5c..49e1ece 100644
--- a/programs/psa/hmac_md_psa.c
+++ b/programs/psa/hmac_md_psa.c
@@ -150,6 +150,7 @@
 
 exit:
     psa_mac_abort( &op );
+    psa_destroy_key( key );
 
     return( status );
 }