sh: Don't set reserved _PAGE_WT bit on SH-3.

Only SH-4 needs to set _PAGE_WT when using write-through caching,
don't attempt to set it on SH-3 where it ends up being a reserved
bit.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/mm/tlb-flush.c

@@ -175,7 +175,7 @@ void update_mmu_cache(struct vm_area_struct *vma,
 
 	/* Set PTEL register */
 	pteval &= _PAGE_FLAGS_HARDWARE_MASK; /* drop software flags */
-#ifdef CONFIG_SH_WRITETHROUGH
+#if defined(CONFIG_SH_WRITETHROUGH) && defined(CONFIG_CPU_SH4)
 	pteval |= _PAGE_WT;
 #endif
 	/* conveniently, we want all the software flags to be 0 anyway */