Fix InstCombine test: invalid CHECK line slipped in r231270

Fix InstCombine test: invalid CHECK line slipped in r231270

I incorrectly wrote CHECK-NEXT with followin with ':', the check was
ignored by FileCheck.
The non-inbound GEP is folded here because the DataLayout is no longer
optional, the fold was originally guarded with a comment that said:
    We need TD information to know the pointer size unless this is inbounds.
Now we always have "TD information" and perform the fold.

Thanks Jonathan Roelofs for noticing.

From: Mehdi Amini <mehdi.amini@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244613 91177308-0d34-0410-b5e6-96231b3b80d8