[PowerPC] Fix typo in vector shuffle combining

a22ecb4 fixed a crash on big endian subtargets. This commit fixes a typo
in that commit which may cause miscompile.

Author: ecnelises

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -14530,7 +14530,7 @@ SDValue PPCTargetLowering::combineVectorShuffle(ShuffleVectorSDNode *SVN,
     unsigned ValidLaneWidth =
         SToVLHS ? SToVLHS.getValueType().getScalarSizeInBits() /
                       LHS.getValueType().getScalarSizeInBits()
-                : SToVRHS.getValueType().getVectorNumElements() /
+                : SToVRHS.getValueType().getScalarSizeInBits() /
                       RHS.getValueType().getScalarSizeInBits();
 
     // Initially assume that neither input is permuted. These will be adjusted