vfio/container: Replace basename with g_path_get_basename

vfio/container: Replace basename with g_path_get_basename

g_path_get_basename() is a portable utility function that has the
advantage of not modifing the string argument. It also fixes a compile
breakage with the Musl C library reported in [1].

[1] https://lore.kernel.org/all/20231212010228.2701544-1-raj.khem@gmail.com/

Reported-by: Khem Raj <raj.khem@gmail.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>