platform/x86: thinkpad_acpi: Fix multi-battery bug

The struct containing the supported operations for all batteries is
being zeroed on each battery probe.  This prevents all other batteries
except the lastly probed one from being configured.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>