Backporting ZTE MF289F introduced an override of DEVICE_PACKAGES for
MF286D, which removed packages needed for built-in modem support.
Fix assignment type to restore those.
Fixes: 3e15a54bb0 ("ipq40xx: Add ZTE MF289F")
Reported-by: Cezary Jackiewicz <cezary@eko.one.pl>
Signed-off-by: Lech Perczak <lech.perczak@gmail.com>