Note that because all of the "switches" will be on until you cover one, you will need diodes on each LDR in order for them to be disambiguated.
Two other things - given that the "on" resistance of the LDR is less than about 7k ohm, which would be less than the effective resistance of the internal pull-ups, you can simply use digital reads and use the internal pull-ups.
Finally, you can "charlieplex" a 4 by 4 keypad if you can wire the keys to suit.