Fixed memory leak by adding Xfree for colormap_ret

Variable "colormap_ret" goes out of scope
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Ander Conselvan de Oliveira <ander.conselvan-de-oliveira@nokia.com>
Signed-off-by: Erkki Seppälä <erkki.seppala@vincit.fi>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>