tools: kwboot: Fix inserting UART data checksum without -B option

tools: kwboot: Fix inserting UART data checksum without -B option

Commit 83a1a335bc84 ("tools: kwboot: Fix parsing UART image without data
checksum") added fixup code to insert place for data checksum if UART image
does not have it. Together with option -B (change baudrate), kwboot
calculates this checksum. Without option -B, it inserts only place for
checksum but does not calculate it.

This commit fix above logic and calculate data checksum also when kwboot is
used without -B option.

Fixes: 83a1a335bc84 ("tools: kwboot: Fix parsing UART image without data checksum")
Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>