pinctrl: mcp23s08: Get rid of legacy platform data

Platform data is a legacy interface to supply device properties
to the driver. In this case we even don't have in-kernel users
for it. Just remove it for good.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200407173849.43628-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>