The current comment fails to clarify why we only accept
the "range limits only" variant of the range descriptor.
Reword it to make some actual sense.

Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Reviewed-by: NManasi Navare <manasi.d.navare@intel.com>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220927170006.27855-2-ville.syrjala@linux.intel.com