vc-cvs-revert: fix off-by-one file mode

* lisp/vc/vc-cvs.el (vc-cvs-revert): 3950 (#o7556) is wrong as
it keeps other-write but disables other-execute permissions.
3949 (#o7555) was intended here.  Use octal notation for clarity.
1 job for master in 61 minutes and 38 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Test
passed #3324
test-all

01:01:38