btrfs: return ptr error from compression workspace

The btrfs compression wrappers translated errors from workspace
allocation to either -ENOMEM or -1.  The compression type workspace
allocators are already returning a ERR_PTR(-ENOMEM).  Just return that
and get rid of the magical -1.

This helps a future patch return errors from the compression wrappers.

Signed-off-by: Zach Brown <zab@redhat.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index d43c544..92371c4 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -887,7 +887,7 @@
 
 	workspace = find_workspace(type);
 	if (IS_ERR(workspace))
-		return -1;
+		return PTR_ERR(workspace);
 
 	ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
 						      start, len, pages,
@@ -923,7 +923,7 @@
 
 	workspace = find_workspace(type);
 	if (IS_ERR(workspace))
-		return -ENOMEM;
+		return PTR_ERR(workspace);
 
 	ret = btrfs_compress_op[type-1]->decompress_biovec(workspace, pages_in,
 							 disk_start,
@@ -945,7 +945,7 @@
 
 	workspace = find_workspace(type);
 	if (IS_ERR(workspace))
-		return -ENOMEM;
+		return PTR_ERR(workspace);
 
 	ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
 						  dest_page, start_byte,