Input: ad714x - add CONFIG_PM_SLEEP to suspend/resume functions

Add CONFIG_PM_SLEEP to suspend/resume functions to fix the following
build warning when CONFIG_PM_SLEEP is not selected. This is because
sleep PM callbacks defined by SIMPLE_DEV_PM_OPS are only used when
the CONFIG_PM_SLEEP is enabled.

drivers/input/misc/ad714x-i2c.c:17:12: warning: 'ad714x_i2c_suspend' defined but not used [-Wunused-function]
drivers/input/misc/ad714x-i2c.c:22:12: warning: 'ad714x_i2c_resume' defined but not used [-Wunused-function]
drivers/input/misc/ad714x-spi.c:20:12: warning: 'ad714x_spi_suspend' defined but not used [-Wunused-function]
drivers/input/misc/ad714x-spi.c:25:12: warning: 'ad714x_spi_resume' defined but not used [-Wunused-function]

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>