drm/i915/i915_scatterlist: Fix kerneldoc formatting issue - missing '@'

drm/i915/i915_scatterlist: Fix kerneldoc formatting issue - missing '@'

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/i915/i915_scatterlist.c:62: warning: Function parameter or member 'size' not described in 'i915_refct_sgt_init'

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230331092607.700644-2-lee@kernel.org