[LoopUnroll] Modify a comment to clarify the usage of TripCount. NFC.

Make it clear that TripCount is the upper bound of the iteration on which
control exits LatchBlock.

Differential Revision: https://reviews.llvm.org/D26675

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290199 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed