test-utils: Avoid undefined behaviour on indirect call

The start method pointer value of the test binding object wasn't well
defined due to the missing memset(). Later conditionals concluded that
the pointer was valid and tried to call through it leading to a crash of
the test binary.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I0e60d1108267f8823f653ae935003a027a13affd
diff --git a/tests/test-utils.c b/tests/test-utils.c
index fa7f460..b475cd6 100644
--- a/tests/test-utils.c
+++ b/tests/test-utils.c
@@ -25,6 +25,7 @@
 	struct mctp_binding_test *test;
 
 	test = __mctp_alloc(sizeof(*test));
+	memset(test, '\0', sizeof(*test));
 	test->binding.name = "test";
 	test->binding.version = 1;
 	test->binding.tx = mctp_binding_test_tx;