pinctrl: mcp23s08: Use for_each_set_bit() and hweight_long()

Here is a simplification of SPI code by using for_each_set_bit() and
hweight_long() library functions.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200407173849.43628-8-andriy.shevchenko@linux.intel.com


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