ACPI: button: Add missing device class clearing on probe failures

ACPI: button: Add missing device class clearing on probe failures

Commit e18947038bf4 ("ACPI: driver: Do not set acpi_device_class()
unnecessarily") modified acpi_button_remove() to clear the device class
field in struct acpi_device on driver removal, but it should also have
updated the rollback path in acpi_button_probe(), which it didn't do,
so do it now.

Fixes: e18947038bf4 ("ACPI: driver: Do not set acpi_device_class() unnecessarily")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Link: https://patch.msgid.link/6167713.MhkbZ0Pkbq@rafael.j.wysocki