serial: 8250_pci: convert to pcim_*() API

The managed API provides a better approach to help with acquiring and releasing
resources. Besides that error handling becomes simpler.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>