[cfi] Fix __cfi_check address calculation.

The current code is incorrect when the target address is 18 bit aligned.

Test: stops random (and extremely rare) crashes in media.extractor
Bug: 63400743
Bug: 65590288

(cherry picked from commit ded4524c)

Change-Id: I7047f7304621d3a7a100cde57860a3154a29effe