serial: imx: Remove unneeded OOM error message

When kzalloc() fails the core MM will already complain about it, so there is
no need to have the error message locally.

Remove the unneeded error message.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>