drm/i915/error: Fixup inactive/active counting

The inactive counter was over the active list, and vice versa.
Fortuitously this should not cause a problem in practice as they shared
the same array and clamped the number of entries they would write.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Reviewed-by: Matthew Auld <matthew.william.auld@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180605160623.30163-1-chris@chris-wilson.co.uk