backlight: da9052: Fix module autoload

The driver has a platform device ID table with multiple device entries,
each setting a different register address in its driver_data to control
the WLED brightness.

But the driver doesn't export these as aliases with MODULE_DEVICE_TABLE()
when the driver is built as a module, instead it just has a single alias
using MODULE_ALIAS("platform:da9052-backlight"). That is clearly wrong
since there isn't a "da9052-backlight" in the platform device ID table,
so if that device name is used, the device won't even match the driver.

So instead of having a wrong alias, export the ones in the dev ID table.

Before this patch:

$ modinfo drivers/video/backlight/da9052_bl.ko | grep alias
alias:          platform:da9052-backlight

After this patch:

$ modinfo drivers/video/backlight/da9052_bl.ko | grep alias
alias:          platform:da9052-wled3
alias:          platform:da9052-wled2
alias:          platform:da9052-wled1

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Acked-by: Jingoo Han <jingoohan1@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>