rtc: asm9260: fix module autoload

If the driver is built as a module, autoload won't work because the module
alias information is not filled so user-space can't match the registered
device with the corresponding module.

Export the module alias information using the MODULE_DEVICE_TABLE() macro.

Before this patch:

$ modinfo drivers/rtc/rtc-asm9260.ko | grep alias
$

After this patch:

$ modinfo drivers/rtc/rtc-asm9260.ko | grep alias
alias:          of:N*T*Calphascale,asm9260-rtcC*
alias:          of:N*T*Calphascale,asm9260-rtc

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>