GRU: fix preprocessor symbol for sparse

Fix preprocessor symbol so that sparse sees it and does not generate
errors:

  drivers/misc/sgi-gru/grutables.h:286:2: error: "Unsupported architecture"
  drivers/misc/sgi-gru/grutables.h:286:2: error: "Unsupported architecture"
  drivers/misc/sgi-gru/grutables.h:286:2: error: "Unsupported architecture"
  drivers/misc/sgi-gru/grutables.h:286:2: error: "Unsupported architecture"
  drivers/misc/sgi-gru/grutlbpurge.c:185:11: error: undefined identifier 'GRUREGION'
  drivers/misc/sgi-gru/grutables.h:286:2: error: "Unsupported architecture"
  drivers/misc/sgi-gru/grutables.h:286:2: error: "Unsupported architecture"

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>