xfs_fsr: convert fsrallfs to use time_t instead of int

xfs_fsr: convert fsrallfs to use time_t instead of int

Convert howlong argument to a time_t as it's truncated to int, but in
practice this is not an issue as duration will never be this big.

Add check for howlong to fit into int (printf can use int format
specifier). Even longer interval doesn't make much sense.

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