OMAPDSS: APPLY: Remove omap_dss_device references in wait_for_go functions

The functions dss_mgr_wait_for_go() and dss_mgr_wait_for_go_ovl() check if there
is an enabled display connected to the manager before trying to see the state of
the GO bit.

The checks related to the display can be replaced by checking the state of the
manager, i.e, whether the manager is enabled or not. This makes more sense than
checking with the connected display as the GO bit behaviour is more connected
with the manager state rather than the display state. A GO bit can only be set
if the manager is enabled. If a manager isn't enabled, we can safely assume that
the GO bit is not set.

Signed-off-by: Archit Taneja <archit@ti.com>