mfd: Replace strict_strtoul() with kstrtoul() in ab* and att*

The usage of strict_strtoul() is not preferred, because
strict_strtoul() is obsolete. Thus, kstrtoul() should be
used.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

diff --cc drivers/mfd/aat2870-core.c
Simple merge

diff --cc drivers/mfd/ab3100-core.c
Simple merge

diff --cc drivers/mfd/ab8500-debugfs.c
Simple merge