[LoopUnroll] Move a simple check earlier. NFC.

Move the check of CallInst earlier to skip expensive recursive operations.

Differential Revision: https://reviews.llvm.org/D23611

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278998 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed