pinctrl: sunxi: fix theoretical uninitialized variable access

gcc warns about a  way that it could use an uninitialized variable:

drivers/pinctrl/sunxi/pinctrl-sunxi.c: In function 'sunxi_pinctrl_init':
drivers/pinctrl/sunxi/pinctrl-sunxi.c:1191:8: error: 'best_div' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This cannot really happen except if 'freq' is UINT_MAX and 'clock' is
zero, and both of these are forbidden. To shut up the warning anyway,
this changes the logic to initialize the return code to the first
divider value before looking at the others.

Fixes: 7c926492 ("pinctrl: sunxi: Add support for interrupt debouncing")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>