Typo decendant => descendant in winaccessibility/MAccessible

Change-Id: I2e49ab149b2bbdad623f8694221b6169cdfd2d9a
Reviewed-on: https://gerrit.libreoffice.org/7706
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>