gpio: eic: sprd: Fix the incorrect EIC offset when toggling

When toggling the level trigger to emulate the edge trigger, the
EIC offset is incorrect without adding the corresponding bank index,
thus fix it.

Fixes: 7bf0d7f6 ("gpio: eic: Add edge trigger emulation for EIC")
Cc: stable@vger.kernel.org
Signed-off-by: Bruce Chen <bruce.chen@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>