extcon: axp288: Use for_each_set_bit() in axp288_extcon_log_rsi()

This simplifies and standardizes axp288_extcon_log_rsi()
by using for_each_set_bit() library function.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>