qemuDomainDiskControllerIsBusy: Fix logic of matching disk bus to controller type

qemuDomainDiskControllerIsBusy: Fix logic of matching disk bus to controller type

The tests which match the disk bus to the controller type were backwards
in this function. This meant that any disk bus type (such as
VIR_DOMAIN_DISK_BUS_SATA) would not skip the controller index comparison
even if the removed controller was of a different type.

Switch the internals to a switch statement with selects the controller
type in the first place and a proper type so that new controller types
are added in the future.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1870072
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>