memory: don't suppress P2M update in populate_physmap()

Commit d18627583d ("memory: don't hand MFN info to translated guests")
wrongly added a null-handle check there - just like stated in its
description for memory_exchange(), the array is also an input for
populate_physmap() (and hence can't reasonably be null). I have no idea
how I've managed to overlook this.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -248,8 +248,7 @@ static void populate_physmap(struct memo
 
             guest_physmap_add_page(d, _gfn(gpfn), _mfn(mfn), a->extent_order);
 
-            if ( !paging_mode_translate(d) &&
-                 !guest_handle_is_null(a->extent_list) )
+            if ( !paging_mode_translate(d) )
             {
                 for ( j = 0; j < (1U << a->extent_order); j++ )
                     set_gpfn_from_mfn(mfn + j, gpfn + j);