ARM: Fix wrong shared bit for CPU write buffer bug test

It is unpredictable to have the same memory mapped using different
shared bit settings for ARMv6 and ARMv7 CPUs.  Fix this for the CPU
write buffer bug test.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/fault-armv.c

@@ -207,9 +207,8 @@ void __init check_writebuffer_bugs(void)
 	page = alloc_page(GFP_KERNEL);
 	if (page) {
 		unsigned long *p1, *p2;
-		pgprot_t prot = __pgprot(L_PTE_PRESENT|L_PTE_YOUNG|
-					 L_PTE_DIRTY|L_PTE_WRITE|
-					 L_PTE_MT_BUFFERABLE);
+		pgprot_t prot = __pgprot_modify(PAGE_KERNEL,
+					L_PTE_MT_MASK, L_PTE_MT_BUFFERABLE);
 
 		p1 = vmap(&page, 1, VM_IOREMAP, prot);
 		p2 = vmap(&page, 1, VM_IOREMAP, prot);