ARM: OMAPFB: panel-sony-acx565akm: fix bad unlock balance

When booting Nokia N900 smartphone with v3.12 + omap2plus_defconfig
(LOCKDEP enabled) and CONFIG_DISPLAY_PANEL_SONY_ACX565AKM enabled,
the following BUG is seen during the boot:

[    7.302154] =====================================
[    7.307128] [ BUG: bad unlock balance detected! ]
[    7.312103] 3.12.0-los.git-2093492-00120-g5e01dc7b #3 Not tainted
[    7.318450] -------------------------------------
[    7.323425] kworker/u2:1/12 is trying to release lock (&ddata->mutex) at:
[    7.330657] [<c031b760>] acx565akm_enable+0x12c/0x18c
[    7.335998] but there are no more locks to release!

Fix by removing double unlock and handling the locking completely inside
acx565akm_panel_power_on() when doing the power on.
Reported-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: stable@vger.kernel.org
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/omap2/displays-new/panel-sony-acx565akm.c

@@ -526,6 +526,8 @@ static int acx565akm_panel_power_on(struct omap_dss_device *dssdev)
 	struct omap_dss_device *in = ddata->in;
 	int r;
 
+	mutex_lock(&ddata->mutex);
+
 	dev_dbg(&ddata->spi->dev, "%s\n", __func__);
 
 	in->ops.sdi->set_timings(in, &ddata->videomode);
@@ -614,10 +616,7 @@ static int acx565akm_enable(struct omap_dss_device *dssdev)
 	if (omapdss_device_is_enabled(dssdev))
 		return 0;
 
-	mutex_lock(&ddata->mutex);
 	r = acx565akm_panel_power_on(dssdev);
-	mutex_unlock(&ddata->mutex);
-
 	if (r)
 		return r;