player can stick to wall

If the player jumps into a wall and keeps holding the d or a key(depending what side of the game the wall is on) they will just stick to the wall.

Is there any code that could prevent this?

my code for the player:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour 
 {
     public float speed;
     public float jumpSpeed;
 
     bool grounded = false;
     public Transform groundcheck;
     float groundRadius = 0.2f;
     public LayerMask whatIsGround;
 
     void FixedUpdate()
     {
         grounded = Physics2D.OverlapCircle (groundcheck.position, groundRadius, whatIsGround);
 
         if(Input.GetKey(KeyCode.D))
         {
             rigidbody2D.velocity = new Vector2 (speed, rigidbody2D.velocity.y);
         }
         else if(Input.GetKey(KeyCode.A))
         {
             rigidbody2D.velocity = new Vector2 (speed*-1, rigidbody2D.velocity.y);
         }
         else
         {
             rigidbody2D.velocity = new Vector2 (0, rigidbody2D.velocity.y);
         }
     }
 
     void Update()
     {
         if(grounded && Input.GetKeyDown(KeyCode.W))
         {
             rigidbody2D.AddForce (new Vector2 (0, jumpSpeed));
         }
     }
 }

Thanks in advance.