OMAPFB: fix compilation error

omapfb compilation fails on x86 (but not on omap):

drivers/video/omap2/omapfb/omapfb-ioctl.c: In function ‘omapfb_ioctl’:
drivers/video/omap2/omapfb/omapfb-ioctl.c:861:23: error: ‘SZ_1M’ undeclared (first use in this function)
drivers/video/omap2/omapfb/omapfb-ioctl.c:861:23: note: each undeclared identifier is reported only once for each function it appears in

Fix this by including linux/sizes.h.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>