[PowerPC][NFC] Fix clang-tidy warning

Reported by
https://results.llvm-merge-guard.org/amd64_debian_testing_clang8-726/clang-tidy.txt

/mnt/disks/ssd0/agent/workspace/amd64_debian_testing_clang8/llvm/lib/Target/PowerPC/PPCISelLowering.cpp:11672:10:
warning: invalid case style for variable 'isEQ'
[readability-identifier-naming]
    bool isEQ = (MI.getOpcode() == PPC::ANDI_rec_1_EQ_BIT ||
         ^~~~
         IsEq
/mnt/disks/ssd0/agent/workspace/amd64_debian_testing_clang8/llvm/lib/Target/PowerPC/PPCISelLowering.cpp:11679:14:
warning: invalid case style for variable 'dl'
[readability-identifier-naming]
    DebugLoc dl = MI.getDebugLoc();
             ^~
             Dl