wizard: Fix typo in dom0 memory configuration

Signed-off-by: Euan Harris <euan.harris@citrix.com>
wizard: Make requested and maximum dom0 RAM equal

It seems best to make the requested and maximum RAM values equal:

   https://lists.xenserver.org/sympa/arc/xs-devel/2013-08/msg00002.html

Signed-off-by: Euan Harris <euan.harris@citrix.com>