dpdk: fix scan-build warnings

dpdk: fix scan-build warnings

runmode-dpdk.c:204:18: warning: Result of 'calloc' is converted to a pointer of type 'char *', which is incompatible with sizeof operand type 'ptrdiff_t' [unix.MallocSizeof]
    args->argv = SCCalloc(capacity, sizeof(ptrdiff_t)); // alloc array of pointers
                 ^~~~~~~~           ~~~~~~~~~~~~~~~~~
./util-mem.h:36:18: note: expanded from macro 'SCCalloc'
 #define SCCalloc calloc
                  ^~~~~~
runmode-dpdk.c:278:16: warning: Result of 'malloc' is converted to a pointer of type 'char *', which is incompatible with sizeof operand type 'char **' [unix.MallocSizeof]
    eal_argv = SCMalloc(args.argc * sizeof(args.argv));
               ^~~~~~~~             ~~~~~~~~~~~~~~~~~
./util-mem.h:35:18: note: expanded from macro 'SCMalloc'
 #define SCMalloc malloc
                  ^~~~~~
2 warnings generated.