examples/vm_power: fix type of cmdline token in cli

examples/vm_power: fix type of cmdline token in cli

Building the example with clang gives the error:

  error: expression which evaluates to zero treated as a null pointer
  constant of type 'const char *' [-Werror,-Wnon-literal-null-conversion]
                        lcore_id, UINT8);
                                  ^~~~~

This error is due to the wrong data type being given for the
cmd_set_cpu_freq_core_num value - it was specified as string rather than
numeric type.

Fixes: f5e5c3347ae3 ("examples/vm_power: cli in guest")
Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: David Hunt <david.hunt@intel.com>