Any wrong or unknown command will result into the output:

 Unknown command '<some text>' - try 'help'

If the command 'help' is disabled, this will end up in:

 Unknown command 'help' - try 'help'

which is for blondes. Suppress the "try 'help'" for the case the 'help'
command is disabled.

Signed-off-by: Juergen Beisert <jbe@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>