Btrfs: fix uninit variable in clone ioctl

Commit 0d97a64e0 creates a new variable but doesn't always set it up.
This puts it back to the original method (key.offset + 1) for the cases
not covered by Filipe's new logic.

Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 97b782f..ca0736c 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3205,7 +3205,7 @@
 	key.offset = off;
 
 	while (1) {
-		u64 next_key_min_offset;
+		u64 next_key_min_offset = key.offset + 1;
 
 		/*
 		 * note the key will change type as we walk through the