fix: incorrect dd command

The bs ins't the image size. rather it's the number of byte that is read
at time. Thus the setting it to something like 1M is enough. And is the
number of times it repeats. Thus setting count to 256 should suffice.

build.bash

@@ -47,7 +47,7 @@ cd busybox-${BUSYBOX_MAJOR}.${BUSYBOX_MINOR}.${BUSYBOX_PATCH}
 cd ..
 
 # Create the bootable image
-dd if=/dev/zero of=dist/boot/boot.img bs=2G count=64
+dd if=/dev/zero of=dist/boot/boot.img bs=1M count=256
 mkfs.ext4 dist/boot/boot.img
 mkdir -p dist/mnt
 sudo mount dist/boot/boot.img dist/mnt