nios2: fix map_physmem to do real cache mapping

Fix the map_physmem() to do real cache mapping.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Acked-by: Marek Vasut <marex@denx.de>
diff --git a/arch/nios2/cpu/cpu.c b/arch/nios2/cpu/cpu.c
index ff0fa20..88c4e18 100644
--- a/arch/nios2/cpu/cpu.c
+++ b/arch/nios2/cpu/cpu.c
@@ -117,7 +117,8 @@
 		"altr,has-initda", 0);
 	gd->arch.has_mmu = fdtdec_get_int(blob, node,
 		"altr,has-mmu", 0);
-	gd->arch.io_region_base = gd->arch.has_mmu ? 0xe0000000 : 0x8000000;
+	gd->arch.io_region_base = gd->arch.has_mmu ? 0xe0000000 : 0x80000000;
+	gd->arch.mem_region_base = gd->arch.has_mmu ? 0xc0000000 : 0x00000000;
 
 	return 0;
 }