xen: arm: initialise the grant_table_gpfn array on allocation

Avoids leaking uninitialised memory via the grant table setup hypercall.

This is XSA-101.

Reported-by: Julien Grall <julien.grall@linaro.org>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 04d0cd0..28ecb13 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -394,7 +394,7 @@ struct domain *alloc_domain_struct(void)
         return NULL;
 
     clear_page(d);
-    d->arch.grant_table_gpfn = xmalloc_array(xen_pfn_t, max_nr_grant_frames);
+    d->arch.grant_table_gpfn = xzalloc_array(xen_pfn_t, max_nr_grant_frames);
     return d;
 }