regex/mlx5: fix memory allocation check
regex/mlx5: fix memory allocation check

The wrong field was checked after allocation.

Fixes: e3dbbf718ebc ("regex/mlx5: support configuration")
Cc: stable@dpdk.org

Signed-off-by: Weiguo Li <9d74fa1db2adfc67cecdb75bdffcce563fe33719@foxmail.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk