pinctrl: fix pinconf_ops::pin_config_dbg_parse_modify kerneldoc

The kerneldoc comment for struct pinconf_ops was missing
pin_config_dbg_parse_modify, and instead described
pin_config_group_dbg_set (which is presumably an old name for the same
function). Rename it in the kerneldoc comment so they match.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>