ARM: imx/mach-apf9328: Simplify UART0 registration

As no flag is passed into UART0 platform data, pass NULL argument
when registering UART0.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>