ACPI: battery: Drop redundant check from acpi_battery_notify()

ACPI: battery: Drop redundant check from acpi_battery_notify()

The battery pointer check against NULL in acpi_battery_notify() is
redundant because the value of that pointer is the one passed to
acpi_dev_install_notify_handler() in acpi_battery_probe() as the
last argument which is not NULL.

Drop the redundant check.

No intentional functional impact.

Closes: https://lore.kernel.org/linux-acpi/aYXvS1h3Bxf_5sCj@stanley.mountain/
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/5981321.DvuYhMxLoT@rafael.j.wysocki