examples/qos_sched: suppress gcc 7.1.1 warning

examples/qos_sched: suppress gcc 7.1.1 warning

This one is more of a compiler issue as application
checks the app_parse_opt_vals() return value.

Since this code is in slow path, adding a memset
to fix following "maybe-uninitialized" warning.

qos_sched/args.c: In function ‘app_parse_args’:
examples/qos_sched/args.c:254:32: error: ‘vals[0]’ may be
used uninitialized in this function [-Werror=maybe-uninitialized]
pconf->rx_port = (uint8_t)vals[0];
                            ~~~~^~~

Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Acked-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>