ARM: s3c24xx: ts: document function argument

Document function argument in kerneldoc comment to fix W=1 compile
warning:

    arch/arm/mach-s3c24xx/setup-ts.c:27: warning: Function parameter or member 'dev' not described in 's3c24xx_ts_cfg_gpio'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>