platform/x86: system76_acpi: Fix input device error handling

platform/x86: system76_acpi: Fix input device error handling

Users on darp6 that do not have Open EC firmware have reported crashes
on boot. Correct the error handling for the input device to fix it.

Managed devices do not need to be explicitly unregistered or freed, as
this is handled by devres. Drop the call to input_free_device.

Fixes: af45cc2f29bd ("platform/x86: system76_acpi: Replace Fn+F2 function for OLED models")
Signed-off-by: Tim Crawford <tcrawford@system76.com>
Link: https://lore.kernel.org/r/20211030154213.2515-1-tcrawford@system76.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>