Fix error message for s_server -psk option

Previously if -psk was given a bad key it would print "Not a hex
number 's_server'".

CLA: Trivial
Reviewed-by: NPaul Yang <yang.yang@baishancloud.com>
Reviewed-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NBen Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/8113)

(cherry picked from commit e57120128fa4e2afa4bda5022a77f73a1e3a0b27)

apps/s_server.c

@@ -1407,7 +1407,7 @@ int s_server_main(int argc, char *argv[])
             for (p = psk_key = opt_arg(); *p; p++) {
                 if (isxdigit(_UC(*p)))
                     continue;
-                BIO_printf(bio_err, "Not a hex number '%s'\n", *argv);
+                BIO_printf(bio_err, "Not a hex number '%s'\n", psk_key);
                 goto end;
             }
             break;