mfd: atmel-smc: Add missing colon(s) for 'conf' arguments

Kerneldoc valication gets confused if syntax isn't "@.*: ".

Adding the missing colons squashes the following W=1 warnings:

drivers/mfd/atmel-smc.c:247: warning: Function parameter or member 'conf' not described in 'atmel_smc_cs_conf_apply'
drivers/mfd/atmel-smc.c:268: warning: Function parameter or member 'conf' not described in 'atmel_hsmc_cs_conf_apply'

Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Ludovic Desroches <ludovic.desroches@microchip.com>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>