uefisign.c: Plug memory leaks.

[delphij]

Summary

Plug memory leaks.

[emaste]

usr.sbin/uefisign/uefisign.c

352–355

early exit would simplify slightly and reduce indentation,

case 'c':
    if (certpath != NULL)
        err(1, "-c can only be specified once");
    certpath = checked_strdup(optarg);
    break;