drm/i915: Fix lock dropping in intel_tv_detect()

When intel_tv_detect() fails to do load detection it would forget to
drop the locks and clean up the acquire context. Fix it up.

This is a regression from:
 commit 208bf9fd


 Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
 Date:   Mon Aug 11 13:15:35 2014 +0300

    drm/i915: Fix locking for intel_enable_pipe_a()

v2: Make the code more readable (Chris)
v3: Drop WARN_ON(type < 0) (Chris)

Cc: stable@vger.kernel.org
Cc: Tibor Billes <tbilles@gmx.com>
Reported-by: Tibor Billes <tbilles@gmx.com>
Tested-by: Tibor Billes <tbilles@gmx.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>