mips: msp71xx/serial: convert to pr_foo() helpers

Convert to pr_foo() helpers rather than printk(KERN_.*).

Acked-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Anoop P <A&lt;Anoop_P.A@pmc-sierra.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>