drm/i915/vbt: flip bta_enabled to bta_disable

The meaning is disable, so flip the member name.

Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/180079eca346edc1671c164da2ca7f428c2ba1de.1754925923.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>