serial: Samsung: Replace printk with dev_* functions

Silences checkpatch warnings regarding use of printks.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>