vdpasim: fix memory leak when freeing IOTLBs

After commit bda324fd ("vdpasim: control virtqueue support"),
vdpasim->iommu became an array of IOTLB, so we should clean the
mappings of each free one by one instead of just deleting the ranges
in the first IOTLB which may leak maps.

Fixes: bda324fd ("vdpasim: control virtqueue support")
Cc: Gautam Dawar <gautam.dawar@xilinx.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20221213090717.61529-1-jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Gautam Dawar <gautam.dawar@amd.com>