serial: imx: fix overrun interrupts in DMA mode

serial: imx: fix overrun interrupts in DMA mode

Commit cf3d96106ba5 ("serial: imx: ensure that RX irqs are off if RX is
off") accidentally enabled overrun interrupts unconditionally when
deferring DMA enable until after the receiver has been enabled during
startup.

Fix this by using the DMA-initialised instead of DMA-enabled flag to
determine whether overrun interrupts should be enabled.

Note that overrun interrupts are already accounted for in
imx_uart_clear_rx_errors() when using DMA since commit b321cca15d20
("serial: imx-serial - update RX error counters when DMA is used").

Fixes: cf3d96106ba5 ("serial: imx: ensure that RX irqs are off if RX is off")
Cc: stable@vger.kernel.org      # 4.17
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20220411081957.7846-1-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>