OMAPDSS: DISPC: Remove usage of dispc_mgr_get_device()

The functions calc_fclk_five_taps() and check_horiz_timing_omap3() use the
function dispc_mgr_get_device() to get the omap_dss_device pointer to which
the manager is connected, the width of the panel is derived from that.

The manager's timing is stored in it's private data in APPLY. This contains
the latest timings applied to the manager. Pass these timings to
dispc_ovl_setup() and use them in the above functions. Remove the function
dispc_mgr_get_device() as it isn't used any more.

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