xfs_repair: make duration take time_t

xfs_repair: make duration take time_t

In most of the uses of duration() takes time_t instead of int.
Convert the rest to use time_t and make duration() take time_t to
not truncate it to int.

While at it remove unnecessary parentheses around 'elapsed'.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>