GRU: fix for debug option

Enable -D DEBUG in the GRU Makefile if CONFIG_SGI_GRU_DEBUG is selected.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>