qemu_domain: Ignore all but SCSI hostdevs in qemuDomainDeviceHostdevDefPostParseResto...

qemu_domain: Ignore all but SCSI hostdevs in qemuDomainDeviceHostdevDefPostParseRestoreBackendAlias()

When retiring QEMU_CAPS_BLOCKDEV_HOSTDEV_SCSI capability the
commit removed a bit too much. Previously, all other devices than
VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_SCSI were ignored in
qemuDomainDeviceHostdevDefPostParseRestoreBackendAlias(). But the
commit in question removed not only the capability check but also
this return early statement. Restore it back.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2129239
Fixes: dc8dbb27d40968c9d9bfad2c6181bccc20c0e44e
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>