platform/x86: fujitsu-laptop: remove redundant safety checks

Do not check whether the pointer passed to ACPI add callbacks is NULL as
it is earlier dereferenced anyway in the bus-level probe callback,
acpi_device_probe().

Do not check the value of acpi_disabled in fujitsu_init(), because it is
already done by acpi_bus_register_driver(), which is the first function
called by fujitsu_init().

Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Reviewed-by: Jonathan Woithe <jwoithe@just42.net>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>