Add missing keyboard shortcut to dialog

Add missing keyboard shortcut to dialog swpossizepage.ui

Change-Id: Ie1e499af05e2a08432dd7649c0ffbe9ea0a12bf2
Reviewed-on: https://gerrit.libreoffice.org/6795
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>