uboot-imx

dfu, nand, ubi: fix erasing after write finish

writting to ubi nand partitions need after write ends an erase
of the remaining sectors. This fail, if dfu write size was not
a multiple of erasesize, example log:

Failure erase: -1

Fix this error.

Signed-off-by: Heiko Schocher <hs@denx.de>