wincng.c: fixed _libssh2_wincng_hash_final return value

_libssh2_wincng_hash_final was returning the internal BCRYPT
status code instead of a valid libssh2 return value (0 or -1).

This also means that _libssh2_wincng_hash never returned 0.

src/wincng.c

@@ -406,7 +406,7 @@ _libssh2_wincng_hash_final(_libssh2_wincng_hash_ctx *ctx,
     ctx->pbHashObject = NULL;
     ctx->dwHashObject = 0;
 
-    return ret;
+    return BCRYPT_SUCCESS(ret) ? 0 : -1;
 }
 
 int