warp7: README: Adjust the binary name after DM conversion

After the conversion to DM the U-Boot binary is called u-boot-dtb.imx,
so fix the README file accordingly.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
diff --git a/board/warp7/README b/board/warp7/README
index 60339da..579bb2d 100644
--- a/board/warp7/README
+++ b/board/warp7/README
@@ -17,7 +17,7 @@
 $ make warp7_config
 $ make
 
-This will generate the U-Boot binary called u-boot.imx.
+This will generate the U-Boot binary called u-boot-dtb.imx.
 
 Put warp7 board in USB download mode: 
 
@@ -28,11 +28,11 @@
 
 Connect a USB cable between the OTG warp7 port and the host PC
 
-Copy u-boot.imx to the imx_usb_loader folder.
+Copy u-boot-dtb.imx to the imx_usb_loader folder.
 
-Load u-boot.imx via USB:
+Load u-boot-dtb.imx via USB:
 
-$ sudo ./imx_usb u-boot.imx
+$ sudo ./imx_usb u-boot-dtb.imx
 
 Then U-Boot should start and its messages will appear in the console program.
 
@@ -46,9 +46,9 @@
 Run the DFU command:
 => dfu 0 mmc 0
 
-Transfer u-boot.imx that will be flashed into the eMMC:
+Transfer u-boot-dtb.imx that will be flashed into the eMMC:
 
-$ sudo dfu-util -D u-boot.imx -a boot
+$ sudo dfu-util -D u-boot-dtb.imx -a boot
 
 Then on the U-Boot prompt the following message should be seen after a
 successful upgrade: