serial: altera-juart: fix NULL device in log message

Add device pointer to port->dev.

Before:

"(NULL device *): ttyJ0 at MMIO 0x1008 (irq = 2, base_baud = 0) is a
Altera JTAG UART"

After:
"altera_jtaguart 1008.serial: ttyJ0 at MMIO 0x1008 (irq = 2, base_baud = 0) is a
Altera JTAG UART"

Signed-off-by: Ley Foon Tan <lftan@altera.com>
Acked-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>