tools/env: allow option "-n" for fw_printenv

In commit bd7b26f8 (Tools: set multiple variable with fw_setenv utility),
the option parsing was changed to getopt_long(3), but option "-n"
of fw_printenv was not included.

This leads to an error message "invalid option -- 'n'" on stderr,
although the output on stdout is correct.

Signed-off-by: Daniel Hobi <daniel.hobi@schmid-telecom.ch>

tools/env/fw_env_main.c

@@ -59,7 +59,7 @@ void usage(void)
 
 	fprintf(stderr, "fw_printenv/fw_setenv, "
 		"a command line interface to U-Boot environment\n\n"
-		"usage:\tfw_printenv\n"
+		"usage:\tfw_printenv [-n] [variable name]\n"
 		"\tfw_setenv [variable name] [variable value]\n"
 		"\tfw_setenv -s [ file ]\n"
 		"\tfw_setenv -s - < [ file ]\n\n"
@@ -93,9 +93,12 @@ main(int argc, char *argv[])
 		cmdname = p + 1;
 	}
 
-	while ((c = getopt_long (argc, argv, "s:h",
+	while ((c = getopt_long (argc, argv, "ns:h",
 		long_options, NULL)) != EOF) {
 		switch (c) {
+		case 'n':
+			/* handled in fw_printenv */
+			break;
 		case 's':
 			script_file = optarg;
 			break;