Staging: sxg: break the build in a cleaner way when !x86

Remove ugly 'Stop Comilation;' statement in sxghif, replace with an
error macro.

This should never be hit as we are only building for x86 boxes at the
moment.

Signed-off by: J.R. Mauro <jrm8005@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>