OMAP: DSS2: Taal: Fix DSI bus locking problem

If omapdss_dsi_display_enable() failed the DSI bus was left locked. Also
if the operation failed later omapdss_dsi_display_disable() would get
called without holding the bus lock.

Signed-off-by: Ville Syrjälä <ville.syrjala@nokia.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>