[js/webgpu] fix maxpool / fp16 (#19981)

Author: guschmue

js/web/lib/wasm/jsep/webgpu/ops/pool.ts

@@ -381,8 +381,9 @@ const createMaxPoolProgramInfo =
           programUniforms
         }),
         getShaderSource: shaderHelper => generatePoolingCode(
-            shaderHelper, x, input.dims.length, outputShape.length, adjustedAttributes, op1, op2, -1e5, uniforms,
-            hasPads, pwStartEndNotZero, phStartEndNotZero),
+            shaderHelper, x, input.dims.length, outputShape.length, adjustedAttributes, op1, op2,
+            (input.dataType === DataType.float16) ? -65504 : -1e5, uniforms, hasPads, pwStartEndNotZero,
+            phStartEndNotZero),
       };
     };