include/linux/gfp.h: convert BUG_ON() into VM_BUG_ON()

VM_BUG_ON() if effectively a BUG_ON() undef #ifdef CONFIG_DEBUG_VM.  That
is exactly what we have here now, and two different folks have suggested
doing it this way.
Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/gfp.h

@@ -249,9 +249,7 @@ static inline enum zone_type gfp_zone(gfp_t flags)
 
 	z = (GFP_ZONE_TABLE >> (bit * ZONES_SHIFT)) &
 					 ((1 << ZONES_SHIFT) - 1);
-#ifdef CONFIG_DEBUG_VM
-	BUG_ON((GFP_ZONE_BAD >> bit) & 1);
-#endif
+	VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
 	return z;
 }