drm/i915: Fix busy ioctl commentary

Just tidy one instance of incorrect context parameter name and a stray
sentence ending from before reporting was converted to be class based.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210611132221.1055650-1-tvrtko.ursulin@linux.intel.com

include/uapi/drm/i915_drm.h

@@ -1348,12 +1348,11 @@ struct drm_i915_gem_busy {
 	 * reading from the object simultaneously.
 	 *
 	 * The value of each engine class is the same as specified in the
-	 * I915_CONTEXT_SET_ENGINES parameter and via perf, i.e.
+	 * I915_CONTEXT_PARAM_ENGINES context parameter and via perf, i.e.
 	 * I915_ENGINE_CLASS_RENDER, I915_ENGINE_CLASS_COPY, etc.
-	 * reported as active itself. Some hardware may have parallel
-	 * execution engines, e.g. multiple media engines, which are
-	 * mapped to the same class identifier and so are not separately
-	 * reported for busyness.
+	 * Some hardware may have parallel execution engines, e.g. multiple
+	 * media engines, which are mapped to the same class identifier and so
+	 * are not separately reported for busyness.
 	 *
 	 * Caveat emptor:
 	 * Only the boolean result of this query is reliable; that is whether