xen/arm: Check return code from fdt_finish_reservemap()

fdt_finish_reservemap() may fail (with -FDT_ERR_NOSPACE) in which case
further DTB creation (in prepare_dtb_hwdom()) makes no sense. Fix it.

Fixes: 13bb63b754 ("device tree,arm: supply a flat device tree to dom0")
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

xen/arch/arm/domain_build.c

@@ -2038,7 +2038,9 @@ static int __init prepare_dtb_hwdom(struct domain *d, struct kernel_info *kinfo)
     if ( ret < 0 )
         goto err;
 
-    fdt_finish_reservemap(kinfo->fdt);
+    ret = fdt_finish_reservemap(kinfo->fdt);
+    if ( ret )
+        goto err;
 
     ret = handle_node(d, kinfo, dt_host, default_p2mt);
     if ( ret )