We had better return the 'err' value when calling kstrtoul() failed, so
the user will know why it really fails, there do little change, let it
return the 'err' value when failed.

Link: https://lkml.kernel.org/r/6329ebe0.050a0220.ec4bd.297cSMTPIN_ADDED_BROKEN@mx.google.comSuggested-by: NSeongJae Park <sj@kernel.org>
Signed-off-by: NXin Hao <xhao@linux.alibaba.com>
Reviewed-by: NSeongJae Park <sj@kernel.org>
Signed-off-by: NSeongJae Park <sj@kernel.org>
Reviewed-by: NXin Hao <xhao@linux.alibaba.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>