Fix "int vs enum" warnings from armcc v5

enumerated type mixed with another type
diff --git a/library/oid.c b/library/oid.c
index 3cca1fa..75b0ee0 100644
--- a/library/oid.c
+++ b/library/oid.c
@@ -367,7 +367,7 @@
     },
     {
         { NULL, 0, NULL, NULL },
-        0, 0,
+        POLARSSL_MD_NONE, POLARSSL_PK_NONE,
     },
 };
 
@@ -401,7 +401,7 @@
     },
     {
         { NULL, 0, NULL, NULL },
-        0,
+        POLARSSL_PK_NONE,
     },
 };
 
@@ -466,7 +466,7 @@
     },
     {
         { NULL, 0, NULL, NULL },
-        0,
+        POLARSSL_ECP_DP_NONE,
     },
 };
 
@@ -496,7 +496,7 @@
     },
     {
         { NULL, 0, NULL, NULL },
-        0,
+        POLARSSL_CIPHER_NONE,
     },
 };
 
@@ -549,7 +549,7 @@
     },
     {
         { NULL, 0, NULL, NULL },
-        0,
+        POLARSSL_MD_NONE,
     },
 };
 
@@ -580,7 +580,7 @@
     },
     {
         { NULL, 0, NULL, NULL },
-        0, 0,
+        POLARSSL_MD_NONE, POLARSSL_CIPHER_NONE,
     },
 };