[ValueTracking] Remove duplicate call to computeKnownBits for the operands of Select.

[ValueTracking] Remove duplicate call to computeKnownBits for the operands of Select.

We call it unconditionally on the operands of the select. Then decide if its a min/max and call it on the min/max operands or on the select operands again. Either of those second calls will overwrite the results of the initial call so we can just delete the first call.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300256 91177308-0d34-0410-b5e6-96231b3b80d8