gpio: sprd: Fix the incorrect data register

Since differnt type EICs have its own data register to read, thus fix the
incorrect data register.

Fixes: 25518e02 ("gpio: Add Spreadtrum EIC driver support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Neo Hou <neo.hou@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>