vPCI/MSI-X: fold clearing of entry->updated

vPCI/MSI-X: fold clearing of entry->updated

Both call sites clear the flag after a successfull call to
update_entry(). This can be simplified by moving the clearing into the
function, onto its success path.

As a result of neither caller caring about update_entry()'s return value
anymore, the function gets switched to return void.

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