[doc] Remove second 'on'
[doc] Remove second 'on'

Signed-off-by: Marno van der Maas <140765e35f75d33bd28eb112371bcce78847cb8a@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan