pinctrl: mcp23s08_spi: Simplify probe()

pinctrl: mcp23s08_spi: Simplify probe()

Simpilfy probe() by replacing device_get_match_data() and ID lookup for
retrieving match data by spi_get_device_match_data().

While at it, replace data type of variable type from 'int'->'unsigned int'
and declare variables following a reverse christmas tree order.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20231001150113.7752-3-biju.das.jz@bp.renesas.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>