misc: don't put nr_cpus into the fsstress -n argument

misc: don't put nr_cpus into the fsstress -n argument

fsstress -n is the number of fs operations per process, not the total
number of operations.  There's no need to factor nr_cpus into the -n
argument because that causes excess runtime as core count increases.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>