pinctrl: tegra: do not export tegra_pinctrl_probe

No user of tegra_pinctrl_probe can be built as a module, hence
exporting the symbol is not necessary. Drop EXPORT_SYMBOL_GPL.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>