drm/i915/perf: Fix use of kernel-doc format in structure members

Insert structure members names into their descriptions to follow
kernel-doc format.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Anna Karas <anna.karas@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190926122158.13028-1-anna.karas@intel.com