tools: mkimage: Do not try to open datafile when it is skipped

When mkimage was instructed to skip datafile via option -s then do not try
to validate or open datafile as it does not have to exist or to be
specified via -d option.

This change allows to use -s option for skipping datafile when -d option
for datafile was not specified.

Signed-off-by: Pali Rohár <pali@kernel.org>
1 file changed