btrfs: replace error code from btrfs_drop_extents

There's a case which clone does not handle and used to BUG_ON instead,
(testcase xfstests/btrfs/035), now returns EINVAL. This error code is
confusing to the ioctl caller, as it normally signifies errorneous
arguments.

Change it to ENOPNOTSUPP which allows a fall back to copy instead of
clone. This does not affect the common reflink operation.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index f2e8fcc..7b001ab 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3088,7 +3088,7 @@
 							 new_key.offset + datal,
 							 1);
 				if (ret) {
-					if (ret != -EINVAL)
+					if (ret != -EOPNOTSUPP)
 						btrfs_abort_transaction(trans,
 								root, ret);
 					btrfs_end_transaction(trans, root);
@@ -3163,7 +3163,7 @@
 							 new_key.offset + datal,
 							 1);
 				if (ret) {
-					if (ret != -EINVAL)
+					if (ret != -EOPNOTSUPP)
 						btrfs_abort_transaction(trans,
 							root, ret);
 					btrfs_end_transaction(trans, root);