app/bbdev: fix null termination in argument parsing
app/bbdev: fix null termination in argument parsing

use snprintf instead of strncpy to ensure null termination when
copying test_vector_filename from cmd arguments.

Coverity issue: 257001
Fixes: f714a18885a6 ("app/testbbdev: add test application for bbdev")

Signed-off-by: Amr Mokhtar <61fd223c159941407afdbb70f082fefb65c9f026@intel.com>

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