drm/rect: Fix drm_rect_rotation_inv() docs

drm/rect: Fix drm_rect_rotation_inv() docs

An overeager sed has corrupted the drm_rect_rotation_inv()
documentation. Fix it up.

Looks like it wasn't entirely correct before the sed fail
either. We were missing _rect_ from the function names, which
also explains why the sed hit these by accident.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180426141631.15798-1-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>