device property: Fix the description of struct fwnode_operations

Adding description for the device_is_available member which
was missing, and fixing the description of the member
property_read_int_array.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>