video: xilinxfb: Fix OF probing on little-endian systems

DTB is always big-endian that's why it is necessary
to properly convert value (*p).
It is automatically done in of_property_read_u32().

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>