[AMDGPU] Use std::min with initializer list. NFC.

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Differential Revision: https://phabricator.intern.facebook.com/D60251704

Author: jayfoad

llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp

@@ -5839,7 +5839,7 @@ unsigned AMDGPUTargetLowering::ComputeNumSignBitsForTargetNode(
     if (Tmp0 == 1)
       return 1; // Early out.
 
-    return std::min(Tmp0, std::min(Tmp1, Tmp2));
+    return std::min({Tmp0, Tmp1, Tmp2});
   }
   default:
     return 1;
@@ -5876,7 +5876,7 @@ unsigned AMDGPUTargetLowering::computeNumSignBitsForTargetInstr(
     unsigned Tmp0 = Analysis.computeNumSignBits(Src0, DemandedElts, Depth + 1);
     if (Tmp0 == 1)
       return 1;
-    return std::min(Tmp0, std::min(Tmp1, Tmp2));
+    return std::min({Tmp0, Tmp1, Tmp2});
   }
   default:
     return 1;