[X86] Use llvm::bit_ceil (NFC)

The argument is known to be nonzero, so we can safely switch to
llvm::bit_ceil.

Author: kazutakahirata

llvm/lib/Target/X86/X86ISelDAGToDAG.cpp

@@ -4181,7 +4181,7 @@ bool X86DAGToDAGISel::tryShrinkShlLogicImm(SDNode *N) {
   if (Opcode == ISD::AND) {
     // Find the smallest zext this could possibly be.
     unsigned ZExtWidth = Cst->getAPIntValue().getActiveBits();
-    ZExtWidth = PowerOf2Ceil(std::max(ZExtWidth, 8U));
+    ZExtWidth = llvm::bit_ceil(std::max(ZExtWidth, 8U));
 
     // Figure out which bits need to be zero to achieve that mask.
     APInt NeededMask = APInt::getLowBitsSet(NVT.getSizeInBits(),