pinctrl: sunxi: Consider pin_base when calculating regulator array index

On most newer Allwinner SoCs, there are two pinctrl devices, the PIO and
R_PIO. PIO covers pin-banks PA to PI (PJ and PK have not been seen),
while R_PIO covers PL to PN. The regulator array only has space for 12
entries, which was designed to cover PA to PL. On the A80, the pin banks
go up to PN, which would be the 14th entry in the regulator array.
However since the driver only needs to track regulators for its own pin
banks, the array only needs to have 9 entries, and also take in to
account the value of pin_base, such that the regulator for the first
pin-bank of the pinctrl device, be it "PA" or "PL" uses the first entry
of the array.

Base the regulator array index on pin_base, such that "PA" for PIO and
"PL" for R_PIO both take the first element within their respective
device's regulator array.

Also decrease the size of the regulator array to 9, just enough to cover
"PA" to "PI".

Fixes: 9a2a566a ("pinctrl: sunxi: Deal with per-bank regulators")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>