pinctrl: th1520: Fix return value for unknown pin error

Fix th1520_pinctrl_dt_node_to_map() to set the return value before
jumping to free_configs when an unknown pin error occurs.

Reported-by: Dan Carpenter <[e-mail]>
Closes: https://lore.kernel.org/r/[e-mail]/
Signed-off-by: Drew Fustini <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/pinctrl-th1520.c

···
 				nmaps = rollback;
 				dev_err(thp->pctl->dev, "%pOFn.%pOFn: unknown pin '%s'\n",
 					np, child, pinname);
+				ret = -EINVAL;
 				goto free_configs;
 			}