Input: colibri-vf50-ts - add missing #include <linux/of.h>

drivers/input/touchscreen/colibri-vf50-ts.c: In function ‘vf50_ts_probe’:
drivers/input/touchscreen/colibri-vf50-ts.c:302: error: implicit declaration of function ‘of_property_read_u32’

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>