pc-dimm: don't assert if pc-dimm alignment != hotpluggable mem range size

Drop superfluous pc-dimm alignment on hot-pluggable mem
range size assert, since it causes QEMU crash during hotplug
when hotplugging pc-dimm with alignment bigger than
an alignment of hot-pluggable mem range size.

Instead allow pc_dimm_get_free_addr() find free address
and bail out gracefully later in that function during
checking if pc-dimm will fit in hot-pluggable mem range.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
