gpio: gpio-aspeed-sgpio: Fix wrong hwirq base in irq handler

Each aspeed sgpio bank has 64 gpio pins(32 input pins and 32 output pins).
The hwirq base for each sgpio bank should be multiples of 64 rather than
multiples of 32.

Signed-off-by: Steven Lee <steven_lee@aspeedtech.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>