package/squid: fix typo

Fixed typo added by
https://git.buildroot.net/buildroot/commit/package/squid?id=d2f7d0d72cd7e00ffbe869011d200f0a4a53e7a5



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>