OMAPDSS: APPLY: clear shadow dirty flags only if GO had been set

In the apply irq handler the code currently clears the shadow dirty
flags whenever the manager in question is not busy (i.e. GO bit is
down). However, this is not quite right, as the GO bit may have never
been set.

While not done in the current code, the above would cause bug in
scenario where the registers are written, and thus shadow_dirty flag is
set, but the GO bit will be set only later. In this case the
shadow_dirty flags would be cleared, even if the HW is not using the new
configurations.

This patch fixes the issue by clearing the shadow flags only when the GO
bit is clear, and the GO bit had been set.

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