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

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@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>