README.hardware: fix the dd command

Add the missing if= prefix for the input image in the dd command.

(From meta-yocto rev: bebe392a37e78f6a00d7ef5c50fe7e14bc187e95)

Signed-off-by: Vivien Didelot <vdidelot@pbsc.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-yocto-bsp/README.hardware

@@ -150,7 +150,7 @@ From a Linux system with access to the image files perform the following steps:
 
   2. Use the "dd" utility to write the image to the SD card. For example:
 
-     # dd core-image-minimal-beaglebone-yocto.wic of=/dev/sdb
+     # dd if=core-image-minimal-beaglebone-yocto.wic of=/dev/sdb
 
   3. Insert the SD card into the Beaglebone and boot the board.