gpio-mt7621 offset fix for 5.10 kernel series

[Peter Naulls]

Looks like there was some code loss when the driver came from an earlier kernel 
series. Without this, my MT7621 board starts its GPIO offsets at 416 (why that
number, I don't know):

--- a/drivers/gpio/gpio-mt7621.c    2022-10-18 15:03:42.596454871 -0400
+++ b/drivers/gpio/gpio-mt7621.c    2022-10-18 13:51:23.628305673 -0400
@@ -234,6 +234,7 @@
          return ret;
      }

+    rg->chip.base = rg->bank * MTK_BANK_WIDTH;
      rg->chip.of_gpio_n_cells = 2;
      rg->chip.of_xlate = mediatek_gpio_xlate;
      rg->chip.label = devm_kasprintf(dev, GFP_KERNEL, "%s-bank%d",


I'm using 5.10 in the current OpenWrt 22.03.

Before

# ls -l /sys/class/gpio/gpiochip4*
lrwxrwxrwx    1 root     root             0 Jan  1  1970 
/sys/class/gpio/gpiochip416 -> 
../../devices/platform/1e000000.palmbus/1e000600.gpio/gpio6
lrwxrwxrwx    1 root     root             0 Jan  1  1970 
/sys/class/gpio/gpiochip448 -> 
../../devices/platform/1e000000.palmbus/1e000600.gpio/gpio8
lrwxrwxrwx    1 root     root             0 Jan  1  1970 
/sys/class/gpio/gpiochip480 -> 
../../devices/platform/1e000000.palmbus/1e000600.gpio/gpio0

After:

# ls -l /sys/class/gpio/
--w-------    1 root     root          4096 Jan  1  1970 export
lrwxrwxrwx    1 root     root             0 Jan  1  1970 gpiochip0 -> 
../../devices/platform/1e000000.palmbus/1e000600.gpio/gpio/gpiochip0
lrwxrwxrwx    1 root     root             0 Jan  1  1970 gpiochip32 -> 
../../devices/platform/1e000000.palmbus/1e000600.gpio/gpio/gpiochip32
lrwxrwxrwx    1 root     root             0 Jan  1  1970 gpiochip64 -> 
../../devices/platform/1e000000.palmbus/1e000600.gpio/gpio/gpiochip64
--w-------    1 root     root          4096 Jan  1  1970 unexport

Which is consistent with what I had in 4.14 series.