minor: use calloc instead of malloc

This data structure needs to be 0'd.

libsel4platsupport/src/io.c

diff --git a/libsel4platsupport/src/io.c b/libsel4platsupport/src/io.c
index 2a0c9ae..249f0d8 100644
--- a/libsel4platsupport/src/io.c
+++ b/libsel4platsupport/src/io.c
@@ -254,7 +254,7 @@
 int
 sel4platsupport_new_io_mapper(vspace_t vspace, vka_t vka, ps_io_mapper_t *io_mapper)
 {
-    sel4platsupport_io_mapper_cookie_t *cookie = malloc(sizeof(sel4platsupport_io_mapper_cookie_t));
+    sel4platsupport_io_mapper_cookie_t *cookie = calloc(1, sizeof(sel4platsupport_io_mapper_cookie_t));
     if (!cookie) {
         ZF_LOGE("Failed to allocate %zu bytes", sizeof(sel4platsupport_io_mapper_cookie_t));
         return -1;