Remove fdatasync when writing to mtd0

When writing to a raw flash device, it's not necessary to do
a sync. Instead, simply closing the file should flush all buffers.
The sync method is not supported and was logging an error when
flashing.

layers/meta-balena-kontron/recipes-support/resin-init/resin-init-flasher-board/resin-init-flasher-board

@@ -10,4 +10,4 @@ set -o errexit
 flash_erase /dev/mtd0 0 0
 
 # Write the image to the SPI NOR flash
-dd if=/mnt/boot/flash.bin of=/dev/mtd0 conv=fdatasync seek=1 bs=1k
+dd if=/mnt/boot/flash.bin of=/dev/mtd0 seek=1 bs=1k