[LoopUnroll] Modify a comment to clarify the usage of TripCount. NFC.
[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: 0ff597fd157e6f4fc38580e8d64ab130330d2411@290199 91177308-0d34-0410-b5e6-96231b3b80d8

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