x86: add table start and end sanity checks to 32-bit init_memory_mapping()

Impact: cleanup

This patch adds a sanity check to the 32-bit version of
init_memory_mapping() to reduce the diff to the 64-bit version.
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1236257708-27269-9-git-send-email-penberg@cs.helsinki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/init_32.c

@@ -1060,7 +1060,7 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
 
 	__flush_tlb_all();
 
-	if (!after_bootmem)
+	if (!after_bootmem && table_end > table_start)
 		reserve_early(table_start << PAGE_SHIFT,
 				 table_end << PAGE_SHIFT, "PGTABLE");