pinctrl: sunxi: Fix a memory leak in 'sunxi_pinctrl_build_state()'

If 'krealloc()' fails, 'pctl->functions' is set to NULL.
We should instead use a temp variable in order to be able to free the
previously allocated memeory, in case of OOM.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>