OMAPFB: Fix possible null pointer dereferencing

Commit 952cbaaa9b8beacc425f9aedf370468cbb737a2c (OMAPFB: Change
dssdev->manager references) added checks for OMAPFB_WAITFORVSYNC ioctl
to verify that the display, output and overlay manager exist. However,
the code erroneously uses && for each part, which means that
OMAPFB_WAITFORVSYNC may crash the kernel if no display, output or
manager is associated with the framebuffer.

This patch fixes the issue by using ||.

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>