perf bench: Fix memory allocation fail check in mem{set,cpy} workloads

perf bench: Fix memory allocation fail check in mem{set,cpy} workloads

Addresses of allocated memory areas saved to '*src' and '*dst', so we
need to check them for NULL, not 'src' and 'dst'.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Cc: Hitoshi Mitake <h.mitake@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1370518503-4230-1-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>