riscv: fixup max_low_pfn with PFN_DOWN.

max_low_pfn should be pfn_size not byte_size.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Signed-off-by: Mao Han <mao_han@c-sky.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/mm/init.c

@@ -28,7 +28,8 @@ static void __init zone_sizes_init(void)
 	unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
 
 #ifdef CONFIG_ZONE_DMA32
-	max_zone_pfns[ZONE_DMA32] = PFN_DOWN(min(4UL * SZ_1G, max_low_pfn));
+	max_zone_pfns[ZONE_DMA32] = PFN_DOWN(min(4UL * SZ_1G,
+			(unsigned long) PFN_PHYS(max_low_pfn)));
 #endif
 	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;