rockchip: doc: update U-Boot location info

Update rockchip U-Boot location to 0x4000/16384.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/doc/README.rockchip b/doc/README.rockchip
index 4b7be0b..9d5af3d 100644
--- a/doc/README.rockchip
+++ b/doc/README.rockchip
@@ -99,13 +99,13 @@
    ./firefly-rk3288/tools/mkimage -n rk3288 -T rksd -d \
 	firefly-rk3288/spl/u-boot-spl-dtb.bin out && \
    sudo dd if=out of=/dev/sdc seek=64 && \
-   sudo dd if=firefly-rk3288/u-boot-dtb.img of=/dev/sdc seek=256
+   sudo dd if=firefly-rk3288/u-boot-dtb.img of=/dev/sdc seek=16384
 
 This puts the Rockchip header and SPL image first and then places the U-Boot
-image at block 256 (i.e. 128KB from the start of the SD card). This
+image at block 16384 (i.e. 4MB from the start of the SD card). This
 corresponds with this setting in U-Boot:
 
-   #define CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR	256
+   #define CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR	0x4000
 
 Put this SD (or micro-SD) card into your board and reset it. You should see
 something like: