drm/omap: dsi: Ensure the device is active during probe

The probe function performs hardware access to read the number of
supported data lanes from a configuration register and thus requires the
device to be active. Ensure this by surrounding the access with
dsi_runtime_get() and dsi_runtime_put() calls.

Fixes: edb715df ("drm/omap: dss: dsi: Move initialization code from bind to probe")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181110111654.4387-4-laurent.pinchart@ideasonboard.com