fs/btrfs: add dependency on BLAKE2 hash

Now btrfs can utilize the newly intorudced BLAKE2 hash.

Signed-off-by: Qu Wenruo <wqu@suse.com>
diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
index a0b48c2..e31afe5 100644
--- a/fs/btrfs/Kconfig
+++ b/fs/btrfs/Kconfig
@@ -6,6 +6,7 @@
 	select ZSTD
 	select RBTREE
 	select SHA256
+	select BLAKE2
 	help
 	  This provides a single-device read-only BTRFS support. BTRFS is a
 	  next-generation Linux file system based on the copy-on-write