Netconsole doesn't have a baudrate. Loady supposes a console has one,
and tries to compute the console's baudrate variable value, regardless
of its existence.

This triggers a NULL pointer dereference on netconsole. If attempting
loady on a netconsole is a bit useless, barebox should not panic. Fix
this by checking the variable exists before reading its value.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>