mbuf: fix truncated strncpy

mbuf: fix truncated strncpy

Gcc-8 discovers issue with platform_mempool_ops.
rte_mbuf_pool_ops.c:26:3: error: ‘strncpy’ output truncated before
  terminating nul copying as many bytes from a string as its length
  [-Werror=stringop-truncation]
  strncpy(mz->addr, ops_name,  strlen(ops_name));

Since the ops_name is already checked for size, using strncpy
here is unnecessary; just use strcpy.

Fixes: a3acc3144a76 ("mbuf: add pool ops selection functions")

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>