gpio: msm: Staticize local variable 'msm_gpio'

The local variable 'msm_gpio' is used only in this file.
Fix the following sparse warning:

drivers/gpio/gpio-msm-v2.c:109:21: warning: symbol 'msm_gpio' was not declared. Should it be static?
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-msm-v2.c

@@ -106,7 +106,7 @@ struct msm_gpio_dev {
 	void __iomem *msm_tlmm_base;
 };
 
-struct msm_gpio_dev msm_gpio;
+static struct msm_gpio_dev msm_gpio;
 
 #define GPIO_INTR_CFG_SU(gpio)    (msm_gpio.msm_tlmm_base + 0x0400 + \
 								(0x04 * (gpio)))