drm/i915/perf: fix gen7_append_oa_reports comment

If I'm going to complain about a back-to-front convention then the least
I can do is not muddle the comment up too.

Signed-off-by: Robert Bragg <robert@sixbynine.org>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170511154345.962-2-lionel.g.landwerlin@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_perf.c

@@ -431,7 +431,7 @@ static int append_oa_sample(struct i915_perf_stream *stream,
  * userspace.
  *
  * Note: reports are consumed from the head, and appended to the
- * tail, so the head chases the tail?... If you think that's mad
+ * tail, so the tail chases the head?... If you think that's mad
  * and back-to-front you're not alone, but this follows the
  * Gen PRM naming convention.
  *