platform/x86: fujitsu: clamp charge_control_end_threshold values to 50

Follow the sysfs ABI documentation that drivers should round written
values to the nearest supported value instead of returning an error.

Tested on a Fujitsu Lifebook U7720.

Signed-off-by: Jelle van der Waa <jvanderwaa@redhat.com>
Reviewed-by: Hans de Goede <hansg@kernel.org>
Acked-by: Jonathan Woithe <jwoithe@just42.net>
Link: https://lore.kernel.org/r/20250609102115.36936-3-jvanderwaa@redhat.com


Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>