pinctrl: pinconf-generic: Remove ti prefix in dev_err messages

It does not make sense to show ti prefix in pinconf_generic_dt_subnode_to_map()
dev_err messages.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>