usb: host: sl811: Switch to use platform_get_mem_or_io()

Switch to use new platform_get_mem_or_io() instead of home grown analogue.
Note, the code has been moved upper in the function to allow farther cleanups,
such as resource sanity check.

Cc: linux-usb@vger.kernel.org
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20201209203642.27648-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>