If hash_calculate is invoked with region_count = 0, it will try to hash
INT_MAX regions. We should check this parameter.
* Avoid a comparison with different signedness.
* Check that region_count is at least 1.
* Avoid a superfluous assignment.
Fixes: b37b46f042cc ("rsa: Use checksum algorithms from struct hash_algo") Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com> Reviewed-by: Simon Glass <sjg@chromium.org>