Revert "drm/i915/perf: Fix warning in documentation"

Userspace portion is still missing.

This reverts commit 9fa6e2f7.

Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181116135510.13807-2-joonas.lahtinen@linux.intel.com

drivers/gpu/drm/i915/i915_perf.c

@@ -345,7 +345,6 @@ static const struct i915_oa_format gen8_plus_oa_formats[I915_OA_FORMAT_MAX] = {
  * @oa_format: An OA unit HW report format
  * @oa_periodic: Whether to enable periodic OA unit sampling
  * @oa_period_exponent: The OA unit sampling period is derived from this
- * @oa_buffer_size_exponent: The OA buffer size is derived from this
  *
  * As read_properties_unlocked() enumerates and validates the properties given
  * to open a stream of metrics the configuration is built up in the structure