Revert "imx: mx6: ddr correct tRFC and tXS"

This reverts commit 059323fb6a8f21637bb617919715c2427f24777c.

This commit 059323fb6a8f21637bb617919715c2427f24777c use JESD79-3E which
is not the newest spec. Should use JESD79-3F in which tRFC is 260ns for
4Gb chip.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Tim Harvey <tharvey@gateworks.com>
diff --git a/arch/arm/cpu/armv7/mx6/ddr.c b/arch/arm/cpu/armv7/mx6/ddr.c
index cf5587b..6b039e4 100644
--- a/arch/arm/cpu/armv7/mx6/ddr.c
+++ b/arch/arm/cpu/armv7/mx6/ddr.c
@@ -702,8 +702,8 @@
 		txs = DIV_ROUND_UP(170000, clkper) - 1;
 		break;
 	case 4: /* 4Gb per chip */
-		trfc = DIV_ROUND_UP(300000, clkper) - 1;
-		txs = DIV_ROUND_UP(310000, clkper) - 1;
+		trfc = DIV_ROUND_UP(260000, clkper) - 1;
+		txs = DIV_ROUND_UP(270000, clkper) - 1;
 		break;
 	case 8: /* 8Gb per chip */
 		trfc = DIV_ROUND_UP(350000, clkper) - 1;