mfd: syscon: Return -ENOSYS if CONFIG_MFD_SYSCON is not enabled

Some platforms may not define CONFIG_MFD_SYSCON (or haven't syscon),
it can fix build error for these platforms.

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
1 file changed