serial_mxc: Remove unconditional DCE setting

serial_mxc: Remove unconditional DCE setting

Commit 83fd908f28c ("dm: imx: serial: Support DTE mode when using driver
model") breaks the serial output for the imx boards that do not use
the serial driver model.

The reason for the breakage is that it's setting UFCR_DCEDTE
unconditionally for the non-dm case.

So keep the original behavior by removing UFCR_DCEDTE setting in the
non-dm case.

Tested on mx7sabresd and mx6wandboard.

Signed-off-by: Breno Lima <breno.lima@nxp.com>
Acked-by: Stefan Agner <stefan.agner@toradex.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>