nd_iostat_start() and nd_iostat_end() implement the same functionality
that generic_start_io_acct() and generic_end_io_acct() already provide.
Change nd_iostat_start() and nd_iostat_end() to call the generic iostat
interfaces. There is no change in the nd interfaces.
Signed-off-by: Toshi Kani <toshi.kani@hpe.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Dave Chinner <david@fromorbit.com> Cc: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>