utils: fs: set return value in ogReduceFs

otherwise error path uses uninitialized variable

 File "/opt/opengnsys/ogClient/src/utils/fs.py", line 112, in ogReduceFs
 return ret
 UnboundLocalError: local variable 'ret' referenced before assignment

src/utils/fs.py

@@ -105,8 +105,9 @@ def ogReduceFs(disk, part):
     elif fstype == 'ntfs':
         ret = _reduce_ntfsresize(partdev)
     else:
-        logging.warn(f'Unable to shrink filesystem at {partdev}. '
-                     f'Unsupported filesystem "{fstype}".')
+        ret = -1
+        logging.error(f'Unable to shrink filesystem at {partdev}. '
+		      f'Unsupported filesystem "{fstype}".')
 
     return ret