Add Linguist comment for translation of Drive-mode.

Translators not familiar with cameras might mistake it for
something related to driving a car.

Change-Id: If54a563a32af537d291b79253056b7b57e108f5b
Reviewed-by: Robert Loehning <robert.loehning@digia.com>
Reviewed-by: Andy Nichols <andy.nichols@digia.com>