src/login.c: Use localtime_r(3) instead of localtime(3)

src/login.c: Use localtime_r(3) instead of localtime(3)

This silences a CodeQL warning.  We don't care about reentrancy, but
after this patch we don't need to break a long line, so that's a win.

Reviewed-by: "Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>