drm/omap: Set rotation property initial value to BIT(DRM_ROTATE_0) insted of 0

0 isn't a valid rotation property value, so let's set the initial value
of the property to BIT(DRM_ROTATE_0) instead.

v2: Drop the BIT()

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Rob Clark <robdclark@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1474907460-10717-7-git-send-email-ville.syrjala@linux.intel.com