x86-64: fix initrd freeing

The comparison of the initrd start address against "&_end" is
unnecessary and incorrect.  Make it match the x86 code that just
compares the passed-in arguments.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/mm/init.c

@@ -531,7 +531,7 @@ void mark_rodata_ro(void)
 #ifdef CONFIG_BLK_DEV_INITRD
 void free_initrd_mem(unsigned long start, unsigned long end)
 {
-	if (start < (unsigned long)&_end)
+	if (start >= end)
 		return;
 	printk ("Freeing initrd memory: %ldk freed\n", (end - start) >> 10);
 	for (; start < end; start += PAGE_SIZE) {