scripts: fix commit check of first word

scripts: fix commit check of first word

The first word of each commit message is checked.
But when the commit range was greater than 1, only the latest commit
was checked.
It is fixed by checking each commit separately.

Fixes: 9c24780f0d5e ("scripts: check first word of commit messages")
Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Tested-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>