platform/x86: fujitsu-laptop: simplify acpi_bus_register_driver() error handling

A separate variable is not needed to handle error codes returned by
acpi_bus_register_driver().  If the latter fails, just use the value it
returned as the value returned by fujitsu_init().

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
[kempniu: rebase patch, rewrite commit message]
Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jonathan Woithe <jwoithe@just42.net>