ACPI: docs: enumeration: Amend PWM enumeration ASL example

Drop blank line and add a closing curly brace to make ASL example closer
to the reality.

Fixes: ef3d13b8

 ("docs: firmware-guide: ACPI: Add a PWM example")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>