chown: fix ownership format string

chown: fix ownership format string

After coreutils rebasing to 9.1, chown(1) behavior changes:
"
   chown and chroot now warn about usages like "chown root.root f",
   which have the nonstandard and long-obsolete "." separator that
   causes problems on platforms where user names contain ".".
   Applications should use ":" instead of ".".
"

https://lwn.net/Articles/891574/

With this behavior change, old format of ownership string will cause
warning like this:
"
+chown: warning: '.' should be ':': '1000.1000'
+.chown: warning: '.' should be ':': '1100.1100'
+.chown: warning: '.' should be ':': '1200.1200'
+.chown: warning: '.' should be ':': '1300.1300'
+.chown: warning: '.' should be ':': '1400.1400'
"

The new format works fine with old versions of coreutils.

Signed-off-by: Murphy Zhou <jencce.kernel@gmail.com>
Reviewed-by: Zorro Lang <zlang@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>