Include what you need: QMap in qvoiceselectorattached_p.h

The class has a QMap (QVariantMap) member, and an inline function
returning said member by value, so it needs QMap in-size. Include the
header.

Amends 3543b7c3b69d69280122958f5949ac7827c543b0 (6.6).

Task-number: QTBUG-145302
Pick-to: 6.11 6.10 6.8
Change-Id: Idbcefd4893cacfceb73dfce4444274a8e41fac95
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>