ash: jobs: Replace some uses of fmtstr with stpcpy/stpncpy

ash: jobs: Replace some uses of fmtstr with stpcpy/stpncpy

Upstream commit:

    Date: Sat, 19 May 2018 02:39:45 +0800
    jobs: Replace some uses of fmtstr with stpcpy/stpncpy

    Some uses of fmtstr, particularly the ones without a format string,
    can be replaced with stpcpy or stpncpy.  This patch does that so
    we don't have to introduce unnecessary format strings in order to
    silence compiler warnings.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>