[IB] mthca: Use enum in mthca_alloc_db() prototype

Make the type parameter of mthca_alloc_db() be an enum mthca_db_type
instead of an int.  This doesn't have any practical effect but
documents the functions a little better.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/drivers/infiniband/hw/mthca/mthca_memfree.c b/drivers/infiniband/hw/mthca/mthca_memfree.c
index 7bd7a4b..d63b1a1 100644
--- a/drivers/infiniband/hw/mthca/mthca_memfree.c
+++ b/drivers/infiniband/hw/mthca/mthca_memfree.c
@@ -487,7 +487,8 @@
 	}
 }
 
-int mthca_alloc_db(struct mthca_dev *dev, int type, u32 qn, __be32 **db)
+int mthca_alloc_db(struct mthca_dev *dev, enum mthca_db_type type,
+		   u32 qn, __be32 **db)
 {
 	int group;
 	int start, end, dir;