gpio: davinci: make davinci_gpio_dev_pm_ops static

This patch fixes the following sprse warnings:

drivers/gpio/gpio-davinci.c:695:1: sparse: warning: symbol 'davinci_gpio_dev_pm_ops' was not declared. Should it be static?

No functional change intended.

Signed-off-by: Min-Hua Chen <minhuadotchen@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>