loader.py: fix 'osv memory' and 'osv mmap' commands

vma layout changed in commit bbec1a1836e15ea42d07dff00cf69a698fe17fb6.

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>