common: map_vcpu_info() cosmetics

common: map_vcpu_info() cosmetics

Use ENXIO instead of EINVAL to cover the two cases of the address not
satisfying the requirements. This will make an issue here better stand
out at the call site.

Also add a missing compat-mode related size check: If the sizes
differed, other code in the function would need changing. Accompany this
by a change to the initial sizeof() expression, tying it to the type of
the variable we're actually after (matching e.g. the alignof() added by
XSA-327).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Julien Grall <jgrall@amazon.com>