env: Correct the offset in uboot.

Currently, we set the env partition offset to 320K in MTD partition
table, however the uboot still picks env partition from 256K offset.
This will fix the "erase 0x9f050000 +0x10000" does not erase env
partition issue.

Change-Id: I9c4da6b53bee1b9e37a05f0c32ce2bac05596c24
diff --git a/include/configs/board953x.h b/include/configs/board953x.h
index 6a6d13b..b2e9956 100755
--- a/include/configs/board953x.h
+++ b/include/configs/board953x.h
@@ -97,7 +97,7 @@
  * Defines to change flash size on reboot
-#define UBOOT_FLASH_SIZE		(256 * 1024)
+#define UBOOT_FLASH_SIZE		(320 * 1024)
 #define CFG_FLASH_MAGIC			0xaabacada