LU-6395 mgc: one byte shorter for logname allocation

LU-6395 mgc: one byte shorter for logname allocation

One byte shorter for logname allocation in mgc_llog_local_copy(),
which might cause buffer overflow in the following sprintf().

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ie758c3650c1cf7848874d9fd3a02a5618043eb8f
Reviewed-on: http://review.whamcloud.com/14146
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>