dediprog: Use unsigned conversions to parse device string

We do neither expect nor support negative device or version numbers.
This also spares us a cast.

Change-Id: I77f56ea0531a7da601362716fe6f937acf312b52
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/92
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
1 file changed