video: vt8500: Adjust contrast in wm8505 framebuffer driver.

The contrast value was typo'd on the original commit (0x80 instead of
0x08). Following feedback from an enduser, a value of 0x10 seems more
suitable due to the default backlight being <100%.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Reviewed-by: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>