libril: use responseInts for LAST_CALL_FAIL_CAUSE on Exynos4

Exynos4 devices send two ints as a response to this request,
causing responseFailCause to think the result is a LastCallFailCause struct,
which it then tries to treat as a Java UTF-8 encoded string, causing a
crash.

Work around this by forcing responseInts (the original behaviour)
on Exynos4 devices.

Change-Id: Ied14948db3049066ffc760b6d3df09b4cefa2df0