pinctrl: rockchip: fix bank's pin_base computing

pinctrl: rockchip: fix bank's pin_base computing

The logic in the core reads the nr_pins of the controller and uses it as
the index of the first pin in the bank (pin_base) it currently parses.
It then increments the number of pins in the controller before going to
the next bank.

This works "fine" for controllers where nr_pins isn't defined in their
rockchip_pin_ctrl struct as it defaults to 0. However, when it is
already set, it'll make the index pin of each bank offset by the number
in nr_pins declared in the struct at initialization, and it'll keep
growing while adding banks, which means the total number of pins in the
controller will be misrepresented.

Additionally, U-Boot proper may probe this driver twice (pre-reloc and
true proper) and not reset nr_pins of the controller in-between meaning
the second probe will have an offset of the actual correct nr_pins.

Instead, let's just store locally the number of pins in the controller
and make sure it's reset between probes.

Finally, this stops modifying a const struct which will soon be
triggering a CPU abort at runtime.

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>