pinctrl: th1520: Fix pinconf return values

pinctrl: th1520: Fix pinconf return values

When Drew took over the pinctrl driver he must have changed
all the -ENOTSUPP returns into -EOPNOTSUPP. This subtle change
was most likely not spotted because it was never mentioned in the
changelog of the patchset, but it breaks all the places in the
pin control and GPIO frameworks where -ENOTSUPP is expected.

Fixes: bed5cd6f8a98 ("pinctrl: Add driver for the T-Head TH1520 SoC")
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Reviewed-by: Drew Fustini <dfustini@tenstorrent.com>
Tested-by: Drew Fustini <dfustini@tenstorrent.com>
Link: https://lore.kernel.org/20241011144826.381104-2-emil.renner.berthing@canonical.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>