When no yamon command line is passed to the kernel, preserve the default

compiled in command line.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/au1000/common/prom.c

@@ -75,6 +75,7 @@ void  prom_init_cmdline(void)
 	}
 	if (cp != &(arcs_cmdline[0])) /* get rid of trailing space */
 		--cp;
+	if (prom_argc > 1)
 		*cp = '\0';
 
 }