cups: use /run instead /var/run in systemd's unit file

/var/run has been deprecated by systemd, so use /run instead,
as suggested by systemd.

(From OE-Core rev: 6c3f56020da7a26c2daea73e39c2f324f1f597db)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-extended/cups/cups.inc

@@ -47,6 +47,7 @@ EXTRA_OECONF = " \
                --enable-debug \
                --disable-relro \
                --enable-libusb \
+               --with-domainsocket=/run/cups/cups.sock \
                DSOFLAGS='${LDFLAGS}' \
                "