plasma-workspace: Fix qttools RDPENDS

Summary:
Fix the RDEPENDS to be qttools-tools instead of qttools. This correctly ensures that qdbus is installed.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

Reviewers: vkrause

Reviewed By: vkrause

Differential Revision: https://phabricator.kde.org/D18203