tools: fix memory leak in hsmtool

Detected by ASan in test_hsmtool_generatehsm:

==58698==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 120 byte(s) in 1 object(s) allocated from:
    #0 0x4e6247 in malloc
    #1 0x7f078452d672 in getdelim

SUMMARY: AddressSanitizer: 120 byte(s) leaked in 1 allocation(s).

Author: morehouse

tools/hsmtool.c

@@ -448,6 +448,7 @@ static void get_words(struct words **words) {
 	if (errno == ERANGE || (errno != 0 && val == 0) || endptr == selected || val < 0 || val >= ARRAY_SIZE(languages))
         errx(ERROR_USAGE, "Invalid language selection, select one from the list [0-6].");
 
+	free(selected);
 	bip39_get_wordlist(languages[val].abbr, words);
 }