pinctrl: mcp23s08: Get rid of spurious level interrupts

pinctrl: mcp23s08: Get rid of spurious level interrupts

irq_mask()/irq_unmask() are not called for nested interrupts. So level
interrupts are never masked, chip's interrupt output is not cleared on
INTCAP or GPIO read, the irq handler is uselessly called again. Nested
irq handler is not called again, because interrupt reason is cleared by
its first call.
/proc/interrupts shows that number of chip's irqs is greater than
number of nested irqs.

This patch adds masking and unmasking level interrupts inside irq handler.

Signed-off-by: Dmitry Mastykin <mastichi@gmail.com>
Link: https://lore.kernel.org/20250122120504.1279790-1-mastichi@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>