staging: lustre: libcfs: discard cfs_time_add/sub

cfs_time_add adds its arguments.
cfs_time_sub subtracts finds the difference.
Discard these and use '+' and '-' directly.

This change highlighted a type error.  The structure field
cr_queued_time was used to store jiffies, but was declared
as time_t (meant for seconds).  So the time is changed to
"unsigned long".

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>