hwmon: (ltc2992) Put fwnode in error case during ->probe()

In each iteration fwnode_for_each_available_child_node() bumps a reference
counting of a loop variable followed by dropping in on a next iteration,

Since in error case the loop is broken, we have to drop a reference count
by ourselves. Do it for port_fwnode in error case during ->probe().

Fixes: b0bd407e

 ("hwmon: (ltc2992) Add support")
Cc: Alexandru Tachici <alexandru.tachici@analog.com>
Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210510100136.3303142-1-andy.shevchenko@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>