ARM: OMAP2+: Fix compile error when FB_OMAP2 is not set

Otherwise we will get:

arch/arm/plat-omap/fb.c:101: error: expected ‘)’ before ‘*’ token

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>