[ARM] S3C24XX: Fix missing s3c_iis_device.

Commit 52da219e removed
the s3c_device_iis, but didn't replace it with anything
so a number of s3c24xx machines are currently failing
to build.

As a temporary fix, re-instate s3c_device_iis until a
proper replacement can be done for it.
Signed-off-by: NBen Dooks <ben-linux@fluff.org>

arch/arm/plat-s3c/include/plat/devs.h

@@ -37,6 +37,7 @@ extern struct platform_device s3c_device_i2c1;
 extern struct platform_device s3c_device_rtc;
 extern struct platform_device s3c_device_adc;
 extern struct platform_device s3c_device_sdi;
+extern struct platform_device s3c_device_iis;
 extern struct platform_device s3c_device_hwmon;
 extern struct platform_device s3c_device_hsmmc0;
 extern struct platform_device s3c_device_hsmmc1;