drm: omapdrm: tiler: Remove unneded module alias for tiler

omap_dmm_tiler.c can't be compiled as a module and it is built
unconditionally as part of omapdrm. Since it can't be used as a module,
there is no need for it to have an unused MODULE_ALIAS().

Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>