leds: netxbig: fix module autoload for OF registration

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/leds//leds-netxbig.ko | grep alias
alias:          platform:leds-netxbig

After this patch:

$ modinfo drivers/leds//leds-netxbig.ko | grep alias
alias:          platform:leds-netxbig
alias:          of:N*T*Clacie,netxbig-ledsC*
alias:          of:N*T*Clacie,netxbig-leds

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>