[InstCombine] Make InstCombiner::OptAndOp take a BinaryOperator instead of an Instruc...

[InstCombine] Make InstCombiner::OptAndOp take a BinaryOperator instead of an Instruction.

The callers have already performed the necessary cast before calling. This allows us to remove a comment that says the instruction must be a BinaryOperator and make it explicit in the argument type.

Had to add a default case to the switch because BinaryOperator::getOpcode() returns a BinaryOps enum.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@299339 91177308-0d34-0410-b5e6-96231b3b80d8