mmc: sdhci-of-at91: 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/mmc/host/sdhci-of-at91.ko | grep alias
$

After this patch:

$ modinfo drivers/mmc/host/sdhci-of-at91.ko | grep alias
alias: of:N*T*Catmel,sama5d2-sdhciC*
alias: of:N*T*Catmel,sama5d2-sdhci

Signed-off-by: Javier Martinez Canillas <[e-mail]>
Acked-by: Ludovic Desroches <[e-mail]>
Acked-by: Adrian Hunter <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/host/sdhci-of-at91.c

···
 	{ .compatible = "atmel,sama5d2-sdhci", .data = &soc_data_sama5d2 },
 	{}
 };
+MODULE_DEVICE_TABLE(of, sdhci_at91_dt_match);
 
 #ifdef CONFIG_PM
 static int sdhci_at91_runtime_suspend(struct device *dev)