OMAPDSS: Correct check for the callback pointer in dss_dsi_disable_pads()

Appear to be a copy-paste bug: the code was checking board_data->dsi_enable_pads
while calling board_data->dsi_disable_pads.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>