mem: Add checks to sendTimingReq in cache
mem: Add checks to sendTimingReq in cache

A small fix to ensure the return value is not ignored.
(transplanted from a16e73f1297f177944f0b8da786e3cd0db8fc628)

LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5