serial: 8250_em: Simplify probe()

Simplify probe() by using dev_err_probe() instead of dev_err() and
add a local variable 'dev' to replace '&pdev->dev'.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20230227114152.22265-3-biju.das.jz@bp.renesas.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>