ANDROID: cfi: Remove unused variable in ptr_to_check_fn

An unused variable will be exposed by a backport of mainline commit
0a5f4176 ("kbuild: clang: disable unused variable warnings only
when constant").

kernel/cfi.c:231:16: warning: unused variable 'check'
[-Wunused-variable]
        unsigned long check;
                      ^
1 warning generated.

Remove it so there is no more warning.

Change-Id: I05a4c20d2a54790991dc1c88c48d8258c548a8cd
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>