[IA64] sanity check reserved region usage

One more trivial, stand-alone patch from the Xen/ia64 review.  Sanity
check usage of the reserved region numbers.
Signed-off-by: NAlex Williamson <alex.williamson@hp.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

arch/ia64/kernel/setup.c

@@ -260,6 +260,7 @@ reserve_memory (void)
 	n++;
 
 	num_rsvd_regions = n;
+	BUG_ON(IA64_MAX_RSVD_REGIONS + 1 < n);
 
 	sort_regions(rsvd_region, num_rsvd_regions);
 }