drm/i915: Fix the confusing comment about the ioctl limits

It was reported that this comment was confusing, and indeed it is.

v2: (one year later!) Add the range for the DRM_I915_* iotcl defines
    (Daniel)
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/uapi/drm/i915_drm.h

@@ -171,8 +171,12 @@ typedef struct _drm_i915_sarea {
 #define I915_BOX_TEXTURE_LOAD  0x8
 #define I915_BOX_LOST_CONTEXT  0x10
 
-/* I915 specific ioctls
- * The device specific ioctl range is 0x40 to 0x79.
+/*
+ * i915 specific ioctls.
+ *
+ * The device specific ioctl range is [DRM_COMMAND_BASE, DRM_COMMAND_END) ie
+ * [0x40, 0xa0) (a0 is excluded). The numbers below are defined as offset
+ * against DRM_COMMAND_BASE and should be between [0x0, 0x60).
  */
 #define DRM_I915_INIT		0x00
 #define DRM_I915_FLUSH		0x01