libxc/unlz4: always set an error return code on failures

"ret", being set to -1 early on, gets cleared by the first invocation
of lz4_decompress()/lz4_decompress_unknownoutputsize(), and hence
subsequent failures wouldn't be noticed by the caller without setting
it back to -1 right after those calls.

Linux commit: 2a1d689c9ba42a6066540fb221b6ecbd6298b728

Reported-by: Matthew Daley <mattjd@xxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/tools/libxc/xc_dom_decompress_lz4.c
+++ b/tools/libxc/xc_dom_decompress_lz4.c
@@ -98,6 +98,7 @@ int xc_try_lz4_decode(
 			goto exit_2;
 		}
 
+		ret = -1;
 		outp += dest_len;
 		size -= chunksize;