luci-lib-chartjs: js linting fixes

luci-lib-chartjs: js linting fixes

fix several variable bleed errors:

  10:194  error    'e' is already defined        no-redeclare
  10:245  error    'g' is already defined        no-redeclare
  11:61   error    'c' is already defined        no-redeclare
  11:395  error    'c[a]' is assigned to itself  no-self-assign
  33:391  error    'c' is already defined        no-redeclare
  35:127  error    'b' is already defined        no-redeclare
  37:128  error    'd' is already defined        no-redeclare
  56:85   error    'c' is already defined        no-redeclare
  56:99   error    'e' is already defined        no-redeclare
  56:127  error    'h' is already defined        no-redeclare

Signed-off-by: Paul Donald <redacted>