video: clps711x: Fix sparse warnings

This patch fixes below warning:

  drivers/video/fbdev/clps711x-fb.c:314:17: warning: incorrect type in initializer (different address spaces)
  drivers/video/fbdev/clps711x-fb.c:314:17:    expected void *__p
  drivers/video/fbdev/clps711x-fb.c:314:17:    got char [noderef] <asn:2>*screen_base

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>