ARM: uniphier: skip memreserve of unused DRAM bank of LD20

Now the "for" loop here iterates on the detected memory banks.
It must skip unused DRAM banks.

Fixes: c995f3a3c526 ("ARM: uniphier: use gd->bd->bi_dram for memory reserve on LD20 SoC")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/arch/arm/mach-uniphier/dram_init.c b/arch/arm/mach-uniphier/dram_init.c
index df0e73a..b9b0cd6 100644
--- a/arch/arm/mach-uniphier/dram_init.c
+++ b/arch/arm/mach-uniphier/dram_init.c
@@ -256,6 +256,9 @@
 		return 0;
 
 	for (i = 0; i < ARRAY_SIZE(gd->bd->bi_dram); i++) {
+		if (!gd->bd->bi_dram[i].size)
+			continue;
+
 		rsv_addr = gd->bd->bi_dram[i].start + gd->bd->bi_dram[i].size;
 		rsv_addr -= rsv_size;