pinctrl: mcp23s08: Fix mcp23x17_regmap initialiser

pinctrl: mcp23s08: Fix mcp23x17_regmap initialiser

The mcp23x17_regmap is initialised with structs named "mcp23x16".
However, the mcp23s08 driver doesn't support the MCP23016 device yet, so
this appears to be a typo.

Fixes: 8f38910ba4f6 ("pinctrl: mcp23s08: switch to regmap caching")
Signed-off-by: Thomas Preston <thomas.preston@codethink.co.uk>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20200828213226.1734264-2-thomas.preston@codethink.co.uk
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>