[mlir][Linalg] Silence warnings in Release builds. NFC.

mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferize.cpp:940:8: warning: unused variable 'opProducesRootRead' [-Wunused-variable]
  bool opProducesRootRead =
       ^
mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferize.cpp:942:8: warning: unused variable 'opProducesRootWrite' [-Wunused-variable]
  bool opProducesRootWrite =
       ^
mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferize.cpp:1498:11: warning: unused variable 'resultNumber' [-Wunused-variable]
  int64_t resultNumber = result.getResultNumber();
          ^
mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferize.cpp:1497:11: warning: unused variable 'operandNumber' [-Wunused-variable]
  int64_t operandNumber = operand.getOperandNumber();
          ^
mlir/lib/Dialect/Linalg/Transforms/ComprehensiveBufferize.cpp:267:20: warning: unused function 'getInPlace' [-Wunused-function]
static InPlaceSpec getInPlace(Value v) {
                   ^