os_map_pci_bar(): unchecked bus_alloc_resource() failure → rman_get_virtual(NULL) NULL-deref panic at device probe

Summary

Both BAR branches never check bus_alloc_resource; the MEMORY branch immediately derefs via the raw rman_get_virtual macro ((r)->r_virtual) - unconditional NULL deref panic at attach; the IOPORT branch survives until the unguarded bus_release_resource in os_unmap_pci_bar. Hardware-gated (no 0x1103 PCI device on guest; driver in-kernel, never attaches). NULL-check + guarded-release fix.