Move free(cmd) to after last use of cmd in intel_gpu_top

Move free(cmd) to after last use of cmd in intel_gpu_top

Error: Use after free (CWE 416)
   Use after free of pointer 'cmd' in call to fprintf
        at line 496 of tools/intel_gpu_top.c in function 'main'.
          Previously freed at line 491 with free.
[ This bug was found by the Parfait 0.4.2 bug checking tool.
  For more information see http://labs.oracle.com/projects/parfait/ ]

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>