minios: grant table map (gntdev) bug fixes
minios: grant table map (gntdev) bug fixes

 * Uninitialized dev_bus_addr argument to GNTTABOP_unmap_grant_ref
   results in an angry hypervisor.
 * Set errno in libxc and return -1 on error.
 * op.status is a int16_t, so it should be printed with PRId16.
 * Don't print domids[0] or refs[0] if the ptr is NULL. It's more
   polite to crash later, after the message has been printed.

Signed-off-by: Diego Ongaro <6fe7e9d8a1492507a9d551576d841127ecd348a8@citrix.com>

rowhit/xen-minios,rowhit/xen-minios,rowhit/xen-minios