mmc: fix missing module license declaration in of_mmc_spi.c

Driver cannot be used as a module without this patch.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/drivers/mmc/host/of_mmc_spi.c b/drivers/mmc/host/of_mmc_spi.c
index 0c44d56..0c7a63c 100644
--- a/drivers/mmc/host/of_mmc_spi.c
+++ b/drivers/mmc/host/of_mmc_spi.c
@@ -22,6 +22,8 @@
 #include <linux/mmc/core.h>
 #include <linux/mmc/host.h>
 
+MODULE_LICENSE("GPL");
+
 enum {
 	CD_GPIO = 0,
 	WP_GPIO,