Doc: Fix formatting of BSD license text

Use \badcode...\endcode instead of \legalese. This fixes the
indentation in the generated page.

This patch amends c095e6ad

.

Change-Id: Idba9af07cab996f40f68c33fbe3579e522fa19c7
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>