serial: 8250_of: Use dev_err_probe() instead of dev_warn()

serial: 8250_of: Use dev_err_probe() instead of dev_warn()

The probe process may generate EPROBE_DEFER. In this case
dev_err_probe() can still record err information. Otherwise
it may pollute logs on that occasion.

This also helps simplifing code and standardizing the error output.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230912165607.402580-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>