video: clps711x: Fix driver build for CONFIG_FB=m

This patch fixes building CLPS711X FB driver if the framebuffer
core is used as a module.

LD init/built-in.o
drivers/built-in.o: In function `clps711x_fb_remove':
:(.text+0x44a8): undefined reference to `unregister_framebuffer'
drivers/built-in.o: In function `clps711x_fb_probe':
:(.text+0x44cc): undefined reference to `fb_get_options'
:(.text+0x45d8): undefined reference to `fb_alloc_cmap'
:(.text+0x45e4): undefined reference to `register_framebuffer'
make: *** [vmlinux] Error 1

Reported-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Alexander Shiyan <[e-mail]>
Signed-off-by: Tomi Valkeinen <[e-mail]>

drivers/video/fbdev/Kconfig

···
 	  unsure, say N.
 
 config FB_CLPS711X_OLD
-	bool
+	tristate
 	select FB_CFB_FILLRECT
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT