serial: imx: Fix DCD reading

serial: imx: Fix DCD reading

commit 4b75f80003617fe35771a9e27022e8fbd6a41875 upstream.

The USR2_DCDIN bit is tested for in register usr1. As the name
suggests the usr2 register should be used instead. This fixes
reading the Carrier detect status.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Fixes: 90ebc4838666 ("serial: imx: repair and complete handshaking")
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>