x86: not clear empty_zero_page again

empty_zero_page is in .bss section, and it is cleared in clear_bss by
x86_64_start_kernel(). So don't clear that again in mem_init
Signed-off-by: NYinghai Lu <yinghai.lu@sun.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

arch/x86/mm/init_64.c

@@ -495,8 +495,7 @@ void __init mem_init(void)
 
 	pci_iommu_alloc();
 
-	/* clear the zero-page */
-	memset(empty_zero_page, 0, PAGE_SIZE);
+	/* clear_bss() already clear the empty_zero_page */
 
 	reservedpages = 0;