pinctrl: sunxi: Fix multiple registration issue

When the support for the PRCM muxer on the A31 has been added, the global
static pinctl_desc definition has been left as is. Unfortunately, this
structure is used to register the pinctrl device, and prior to this
registration, we set the name and pins field.

Since this structure is shared across instances, that means that the latest
registered pinctrl device wins in setting the name, pins and pins numbers,
which is not really a good thing.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>