gpio: omap: Remove set but not used variable 'dev'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpio/gpio-omap.c: In function 'gpio_omap_cpu_notifier':
drivers/gpio/gpio-omap.c:1327:17: warning:
 variable 'dev' set but not used [-Wunused-but-set-variable]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>