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: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/sxg/sxghif.h

@@ -854,5 +854,5 @@ struct SXG_SCATTER_GATHER {
 #define SXG_SGL_BUFFER(_SxgSgl)		NULL
 #define SXG_SGL_BUF_SIZE			0
 #else
-Stop Compilation;
+#error staging: sxg: driver is for X86 only!
 #endif