gpio: mmio: do not calculate bgpio_bits via "ngpios"

bgpio_bits must be aligned with the data bus width. For example, on a
32 bit big endian system and we only have 16 GPIOs. If we only assume
bgpio_bits=16 we can never control the GPIO because the base address
is the lowest address.

low address                          high address
-------------------------------------------------
|   byte3   |   byte2   |   byte1   |   byte0   |
-------------------------------------------------
|    NaN    |    NaN    |  gpio8-15 |  gpio0-7  |
-------------------------------------------------

Fixes: 55b2395 ("gpio: mmio: handle "ngpios" properly in bgpio_init()")
Fixes: openwrt/openwrt#15739
Reported-by: Mark Mentovai <[email protected]>
Signed-off-by: Shiji Yang <[email protected]>
Suggested-By: Mark Mentovai <[email protected]>
Reviewed-by: Jonas Gorski <[email protected]>
Tested-by: Lóránd Horváth <[email protected]>
Reviewed-by: Linus Walleij <[email protected]>
Link: https://lore.kernel.org/r/TYCP286MB089577B47D70F0AB25ABA6F5BCD52@TYCP286MB0895.JPNP286.PROD.OUTLOOK.COM
Signed-off-by: Bartosz Golaszewski <[email protected]>

Author: DragonBluep

drivers/gpio/gpio-mmio.c

@@ -619,8 +619,6 @@ int bgpio_init(struct gpio_chip *gc, struct device *dev,
 	ret = gpiochip_get_ngpios(gc, dev);
 	if (ret)
 		gc->ngpio = gc->bgpio_bits;
-	else
-		gc->bgpio_bits = roundup_pow_of_two(round_up(gc->ngpio, 8));
 
 	ret = bgpio_setup_io(gc, dat, set, clr, flags);
 	if (ret)