ARM: i.MX53: UARTn_CTS pin should not change RTS input select

If both the RTS pad and CTS pad definitions setup
IOMUXC_UARTn_IPP_UART_RTS_MUX_SELECT_INPUT, then
the order of setup will matter. We don't want that.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>