btrfs: fix some error checking for btrfs_decompress()

The btrfs_decompress() function mostly (u32)-1 on error but it can
also return -EPERM or other kernel error codes from zstd_decompress().
The "ret" variable is an int, so we could just check for negatives.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Qu Wenruo <wqu@suse.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 38e285b..4691612 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -390,7 +390,7 @@
 			   csize);
 	ret = btrfs_decompress(btrfs_file_extent_compression(leaf, fi),
 			       cbuf, csize, dbuf, dsize);
-	if (ret == (u32)-1) {
+	if (ret < 0) {
 		ret = -EIO;
 		goto out;
 	}
@@ -500,7 +500,7 @@
 
 	ret = btrfs_decompress(btrfs_file_extent_compression(leaf, fi), cbuf,
 			       csize, dbuf, dsize);
-	if (ret == (u32)-1) {
+	if (ret < 0) {
 		ret = -EIO;
 		goto out;
 	}