drm/panel/panel-raspberrypi-touchscreen: Demote kernel-doc abuse

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

 drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c:33: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Eric Anholt <eric@anholt.net>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602143300.2330146-21-lee.jones@linaro.org

drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c

@@ -29,7 +29,7 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
-/**
+/*
  * Raspberry Pi 7" touchscreen panel driver.
  *
  * The 7" touchscreen consists of a DPI LCD panel, a Toshiba