OMAPDSS: fix paddr check for TILER addresses

The DISPC driver checks that the buffer address is not 0. However, when
using TILER, the address space is TILER specific and 0 is a valid
address.

Fix the check to allow address of 0 for TILER.

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