gpio_msm: Fix build error due to missing err.h

drivers/gpio/gpio-msm-v1.c: In function 'gpio_msm_v1_probe':
drivers/gpio/gpio-msm-v1.c:656:2:
error: implicit declaration of function 'IS_ERR'
[-Werror=implicit-function-declaration]
drivers/gpio/gpio-msm-v1.c:657:3:
error: implicit declaration of function 'PTR_ERR'
[-Werror=implicit-function-declaration]

This driver failed to compile after commit 68515bbe
(gpio_msm: Convert to use devm_ioremap_resource,
2013-06-10).

Acked-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>