kernel-install: exit with option --json=help (#39974)

In that case, `parse_json_argument()` returns 0.

Follow-up for bdd36c003d9c4c4ca89c92be504615378f61513c (v255).

src/kernel-install/kernel-install.c

@@ -1621,7 +1621,7 @@ static int parse_argv(int argc, char *argv[], Context *c) {
 
                 case ARG_JSON:
                         r = parse_json_argument(optarg, &arg_json_format_flags);
-                        if (r < 0)
+                        if (r <= 0)
                                 return r;
                         break;
 

src/shared/cryptsetup-util.c

@@ -298,7 +298,7 @@ int dlopen_cryptsetup(void) {
 
         return 1;
 #else
-        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "cryptsetup support is not compiled in.");
+        return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "cryptsetup support is not compiled in.");
 #endif
 }