If xc_gntshr_open failed the only thing to cleanup is free allocated
memory. So instead of calling libxenvchan_close (which assume
valid calculated buffers being mmaped already) free memory and return.
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>