HACK: OMAP: DSS2: add delay after enabling clocks

On omap4 the registers may not be accessible right after enabling the
clocks. At some point this will be handled by pm_runtime, but, for the
time begin, adding a small delay after clk_enable() should make things
work.

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