Fix minor compile errors

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 3242232..5781fe0 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -349,7 +349,8 @@
             TEST_ASSERT( mbedtls_x509write_crt_set_ns_cert_type( &crt, cert_type ) == 0 );
         if( strcmp( ext_key_usage, "NULL" ) != 0 )
         {
-            mbedtls_asn1_sequence exts[2] = { };
+            mbedtls_asn1_sequence exts[2];
+            memset(exts, 0, sizeof(exts));
 #define SET_OID(x, oid) \
     do { x.len = MBEDTLS_OID_SIZE(oid); x.p = (unsigned char*)oid; \
          x.tag = MBEDTLS_ASN1_OID; } while( 0 )