xen/arm: Fix initrd placeholders generation in make_chosen_node()

When booting a dom0less domU without initial ramdisk, it was observed
that Xen still creates empty linux,initrd-{start,end} properties under
/chosen node. This is because in make_chosen_node(), generation of initrd
placeholders (later on filled with the real values) is protected with
a check for presence of kernel bootmodule (always present) instead of
initrd bootmodule. Fix it along with renaming the variable from "mod" to
"initrd" to prevent similar mistakes in the future.

Fixes: 48f4bf6bde ("arm/acpi: Create min DT stub for Dom0")
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/domain_build.c

@@ -2256,7 +2256,7 @@ int __init make_chosen_node(const struct kernel_info *kinfo)
 {
     int res;
     const char *bootargs = NULL;
-    const struct bootmodule *mod = kinfo->kernel_bootmodule;
+    const struct bootmodule *initrd = kinfo->initrd_bootmodule;
     void *fdt = kinfo->fdt;
 
     dt_dprintk("Create chosen node\n");
@@ -2276,7 +2276,7 @@ int __init make_chosen_node(const struct kernel_info *kinfo)
      * If the bootloader provides an initrd, we must create a placeholder
      * for the initrd properties. The values will be replaced later.
      */
-    if ( mod && mod->size )
+    if ( initrd && initrd->size )
     {
         u64 a = 0;
         res = fdt_property(kinfo->fdt, "linux,initrd-start", &a, sizeof(a));