hwmon: (ltc2992) Fix memory leak in ltc2992_parse_dt()

A new error path was added to the fwnode_for_each_available_node() loop
in ltc2992_parse_dt(), which leads to an early return that requires a
call to fwnode_handle_put() to avoid a memory leak in that case.

Add the missing fwnode_handle_put() in the error path from a zero value
shunt resistor.

Cc: stable@vger.kernel.org
Fixes: 10b02902

 ("hwmon: (ltc2992) Avoid division by zero")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://lore.kernel.org/r/20240523-fwnode_for_each_available_child_node_scoped-v2-1-701f3a03f2fb@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>