gpio: pmic-eic-sprd: Add can_sleep flag for PMIC EIC chip

gpio: pmic-eic-sprd: Add can_sleep flag for PMIC EIC chip

The drivers uses a mutex and I2C bus access in its PMIC EIC chip
get implementation. This means these functions can sleep and the PMIC EIC
chip should set the can_sleep property to true.

This will ensure that a warning is printed when trying to get the
value from a context that potentially can't sleep.

Fixes: 348f3cde84ab ("gpio: Add Spreadtrum PMIC EIC driver support")
Signed-off-by: Wenhua Lin <Wenhua.Lin@unisoc.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>